Featured Catholic tradition, not the Bible, teaches a change to Sundaykeeping.

If you study your Bible, you will find this compromise between paganism and Christianity resulted in the development of "the man of sin" foretold in prophecy as opposing and exalting himself above God.

2 Thessalonians 2:2-3 King James Version (KJV)
3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.

What happened next can only be the "Great Apostasy" as we read from Wikipedia. "
The Great Apostasy is a term used by some religious groups to describe the perceived fallen state of traditional Christianity, especially the Roman Catholic Church, because they claim it allowed traditional Greco-Roman culture (i.e.Greco-Roman mysteries, deities of solar monism such as Mithras and Sol Invictus, pagan festivals and Mithraic sun worship and idol worship) into the church. That it is not representative of the faith founded by Jesus and promulgated through his twelve Apostles: in short, in their opinion, the church has fallen into apostasy.[1][2] They feel that to attract the pagans to nominal Christianity, the Catholic Church took measures to amalgamate the Christian and pagan festivals so pagans would join the church;[3] for example, bringing in the pagan festival of Easter as a substitute for the Pasch or Passover, although neither Jesus nor his Apostles enjoined the keeping of this or any other festival.[4][5]

They consider the Papacy to be in full-blown apostasy for allowing pagan rituals, the worship of Mary and idols[6], and pagan beliefs and ceremonies to come into the church, having those who pointed out its apostasy persecuted and killed and never repenting of or fully admitting the true extent of its actions.[7][8][9][10]"

Many pagans worshiped the sun and other pagan gods as they thought that their sun gods and fertility goddesses died at the winter solstice and came back to life at the spring equinox. Baal worship is sun worship, and Ashtoreth / Ishtar / Astarte is the queen of heaven. These pagan gods had spread through Egyptian/Greek influence and spread throughout the known Roman world.

Note what it says in Judges:
"Judges 2:13 And they forsook the LORD, and served Baal and Ashtaroth."

 

Read your Bible, if you look you will we see that Paul kept the Sabbath.

"And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures." Acts 17:2. "Paul and his company ... went into the synagogue on the sabbath day, and sat down." Acts 13:13, 14. "And on the sabbath we went out of the city by a river side, where prayer was wont to be made; and we sat down, and spake unto the women which resorted thither." Acts 16:13. "And he [Paul] reasoned in the synagogue every sabbath, and persuaded the Jews and the Greeks." Acts 18:4.

And so did the Apostles and Early Church, but a apostate church claims it has the authority to change this, so everyone has to open their eyes and see the truth of the matter.

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Please, read your history and its everywhere....

"Until well into the second century we do not find the slightest indication in our sources that Christians marked Sunday by any kind of abstention from work."

--W. Rordorf, Sunday, p. 157.

“The festival of Sunday, like all other festivals, was always only a human ordinance, and it was far from the intentions of the apostles to establish a divine command in this respect, far from them, and from the early apostolic church, to transfer the laws of the Sabbath to Sunday. Perhaps at the end of the second century a false application of this kind had begun to take place; for men appear by that time to have considered laboring on Sunday as a sin.”

Neander’s Church History, translated by H. J. Rose, p. 186.

"Cults of the sun, as we know from many sources, had attained great vogue during the second, third, and fourth centuries. Sun-worshipers indeed formed one of the big groups in that religious world in which Christianity was fighting for a place. Many of them became converts to Christianity . . . Worshipers in St. Peter's turned away from the altar and faced the door so that they could adore the rising sun."

--Gordon J. Laing, Survivals of Roman Religion, p. 192. [Dr. Laing(1869-1945) was a Canadian-born university professor and later dean at the University of Chicago].

"North African half-heathen Christians who led out in Christian worship on Sunday, were also the first to call Jesus Christ the true Sun-god, and to direct their prayers toward the east--the rising sun--to rise early in the morning that they pray facing the sun as it arose. Clement of Alexandria (c. 150-215 AD.) frequently called Christ the true Sun, and he urged the pagans to accept Him as such. Origen (c. 185-254) said, "Christ is the Sun of Justice; if the moon is united, which is the Church, it will be filled with His light." Cyprian (d. 258), Bishop of Carthage told believers "to pray at sunrise to commemorate the resurrection . . . and to pray at the setting of the sun . . . for the advent of Christ." "They took a much easier view of certain pagan customs, conventions and images and saw no objection, after ridding them of their pagan content, to adapting them to Christian thought."

--J. Danielou, Bible and Liturgy, p. 299.

“ The next step in addition to this was the adoption of the day of the sun as a festival day. To such an extent were the forms of sun-worship practised in this apostasy, that before the close of the second century the heathen themselves charged these so-called Christians with worshiping the sun. A presbyter of the church of Carthage, then and now one of the “church fathers,” who wrote about A.D. 200, considered it necessary to make a defense of the practice, which he did to the following effect in an address to the rulers and magistrates of the Roman Empire: — “Others, again, certainly with more information and greater verisimilitude, believe that the sun is our god. We shall be counted Persians perhaps, though we do not worship the orb of day painted on a piece of linen cloth, having himself everywhere in his own disk. The idea no doubt has originated from our being known to turn to the east in prayer. But you, many of you, also under pretense sometimes of worshiping the heavenly bodies, move your lips in the direction of the sunrise. In the same way, if we devote Sunday to rejoicing, from a far different reason than sun-worship, we have some resemblance to those of you who devote the day of Saturn to ease and luxury, though they too go far away from Jewish ways, of which indeed they are ignorant.” — Tertullian “Apology,” chap. 16.

And again in an address to all the heathen he justifies this practice by the argument, in effect, You do the same thing, you originated it too, therefore you have no right to blame us. In his own words his defense is as follows: —

“Others, with greater regard to good manners, it must be confessed, suppose that the sun is the god of the Christians, because it is a well-known fact that we pray toward the east, or because we make Sunday a day of festivity. What then? Do you do
less than this? Do not many among you, with an affectation of sometimes worshiping the heavenly bodies, likewise move your lips in the direction of the sunrise? It is you, at all events, who have admitted the sun into the calendar of the week; and you have selected its day, in preference to the preceding day, as the most suitable in the week for either an entire abstinence from the bath, or for its postponement until the evening, or for taking rest and banqueting.” — Tertullian “Ad Nationes,” book 1, chap. 13.

This accommodation was easily made, and all this practice was easily justified, by the perverse-minded teachers, in the perversion of such scriptures as, “The Lord God is a sun and shield,” and, “Unto you that fear my name shall the Sun of Righteousness arise with healing in his wings.” As this custom spread, and through it such disciples were multiplied, the ambition of the bishop of Rome grew apace. It was in honor of the day of the sun that there was manifested the first attempt of the bishop of Rome to compel the obedience of all other bishops, and the fact that this attempt was made in such a cause, at the very time when these pretended Christians were openly accused by the heathen of worshiping the sun, is strongly suggestive.

From Rome there came now another addition to the sun-worshiping apostasy. The first Christians being mostly Jews, continued to celebrate the Passover in remembrance of the death of Christ, the true Passover; and this was continued among those who from among the Gentiles had turned to Christ. Accordingly, the celebration was always on the Passover day, — the fourteenth of the first month. Rome, however, and from her all the West, adopted the day of the sun as the day of this celebration. According to the Eastern custom, the celebration, being on the fourteenth day of the month, would of course fall on different days of the week as the years revolved. The rule of Rome was that the celebration must always be on a Sunday — the Sunday nearest to the fourteenth day of the first month of the Jewish year. And if the fourteenth day of that month should itself be a Sunday, then the celebration was not to be held on that day, but upon the next Sunday. One reason of this was not only to be as like the heathen as possible, but to be as un like the Jews as possible; this, in order not only to facilitate the “conversion” of the heathen by conforming to their customs, but also by pandering to their spirit of contempt and hatred of the Jews. It was upon this point that the bishop of Rome made his first open attempt at Absolutism………………………………..................

“Accordingly, after having taken the advice of some foreign bishops, he wrote an imperious letter to the Asiatic prelates commanding them to imitate the example of the Western Christians with respect to the time of celebrating the festival of Easter. The Asiatics answered this lordly requisition by the pen of Polycrates, bishop of Ephesus, who declared in their name, with great spirit and resolution, that they would by no means depart in this manner from the custom handed down to them by their ancestors. Upon this the thunder of excommunication began to roar. Victor, exasperated by this resolute answer of the Asiatic bishops, broke communion with them, pronounced them unworthy of the name of his brethren, and excluded them from all fellowship with the church of Rome.” — Mosheim “Ecclesiastical History,” century 2, part 2, chap. 4, par. 11. Maclaine’s Translation………………………

 

..."While this effort was being made on the side of philosophy to unite all religions, there was at the same time a like effort on the side of politics. It was the ambition of Elagabalus (A.D. 218-222) to make the worship of the sun supersede all other worship in Rome. It is further related of him that a more ambitious scheme even than this was in the emperor’s mind; which was nothing less than the blending of all religions into one, of which “the sun was to be the central object of adoration.” — Milman “History of Christianity” book 2, chap. 8, par. 22.


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"Modern Christians who talk of keeping Sunday as a 'holy' day, as in the still extant 'Blue Laws,' of colonial America, should know that as a 'holy' day of rest and cessation from labor and amusements Sunday was unknown to Jesus . . . It formed no tenet [teaching] of the primitive Church and became 'sacred' only in the course of time. Outside the Church its observance was legalized for the Roman Empire through a series of decrees starting with the famous one of Constantine in 321, an edict due to his political and social ideas."[/b

]--W, W. Hyde, "Paganism to Christianity in the Roman Empire," 1946, p. 257.

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"The Church made a sacred day of Sunday . . . largely because it was the weekly festival of the sun;--for it was a definite Christian policy to take over the pagan festivals endeared to the people by tradition, and to give them a Christian significance."

-- Arthur Weigall, "The Paganism in Our Christianity," 1928, p. 145.

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"Remains of the struggle [between the religion of Christianity and the religion of Mithraism] are found in two institutions adopted from its rival by Christianity in the fourth century, the two Mithraic sacred days: December 25, 'dies natalis solis' [birthday of the sun], as the birthday of Jesus,--and Sunday, 'the venerable day of the Sun,' as Constantine called it in his edict of 321."

--Walter Woodburn Hyde, "Paganism to Christianity in the Roman Empire," p. 60.

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"This [Constantine's Sunday decree of March, 321] is the 'parent' Sunday law making it a day of rest and release from labor. For from that time to the present there have been decrees about the observance of Sunday which have profoundly influenced European and American society. When the Church became a part of State under the Christian emperors, Sunday observance was enforced by civil statutes, and later when the Empire was past, the Church, in the hands of the papacy, enforced it by ecclesiastical and also by civil enactments."

--Walter W. Hyde, "Paganism to Christianity in the Roman Empire," 1946, p. 261.

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"Constantine labored at this time untiringly to unite the worshipers of the old and the new into one religion. All his laws and contrivances are aimed at promoting this amalgamation of religions. He would by all lawful and peaceable means melt together a purified heathenism and a moderated Christianity . . . Of all his blending and melting together of Christianity and heathenism, none is more easy to see through than this making of his Sunday law: The Christians worshiped their Christ, the heathen their Sun-god. . . [so they should now be combined."

--H.G. Heggtveit, "illustreret Kirkehistorie," 1895, p. 202.

"As we have already noted, excepting for the Roman and Alexandrian Christians, the majority of Christians were observing the seventh-day Sabbath at least as late as the middle of the fifth century [A.D. 450]. The Roman and Alexandrian Christians were among those converted from heathenism. They began observing Sunday as a merry religious festival in honor of the Lord's resurrection, about the latter half of the second century A.D. However, they did not try to teach that the Lord or His apostles commanded it. In fact, no ecclesiastical writer before Eusebius of Caesarea in the fourth century even suggested that either Christ or His apostles instituted the observance of the first day of the week.

"These Gentile Christians of Rome and Alexandria began calling the first day of the week 'the Lord's day.' This was not difficult for the pagans of the Roman Empire who were steeped in sun worship to accept, because they [the pagans] referred to their sun-god as their 'Lord.'

"--EM. Chalmers, "How Sunday Came Into the Christian Church," p. 3.

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"Down even to the fifth century the observance of the Jewish Sabbath was continued in the Christian church, but with a rigor and solemnity gradually diminishing until it was wholly discontinued."

--Lyman Coleman, "Ancient Christianity Exemplified" chap. 26, sec. 2, p. 527.

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"What began, however, as a pagan ordinance, ended as a Christian regulation; and a long series of imperial decrees, during the fourth, fifth, and sixth centuries, enjoined with increasing stringency abstinence from labor on Sunday."

--Huttan Webster, "Rest Days," pp. 122-123, 210.

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"A history of the problem shows that in some places, it was really only after some centuries that the Sabbath rest really was entirely abolished, and by that time the practice of observing a bodily rest on the Sunday had taken its place . . . It was the seventh day of the week which typified the rest of God after creation, and not the first day. "

--Vincent Jo Kelly, Forbidden Sunday and Feast day Occupations, 1943, pp. 15, 22 [This Catholic University Press publication was written by a priest of the Redemptorist order].

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"The early Christians had at first adopted the Jewish seven-day week with its numbered week days, but by the close of the third century A.D. this began to give way to the planetary week; and in the fourth and fifth centuries the pagan designations became generally accepted in the western half of Christendom. The use of the planetary names by Christians attests the growing influence of astrological speculations introduced by converts from paganism . . . During these same centuries the spread of Oriental solar [sun] worships, especially that of Mithra [Persian sun worship], in the Roman world, had already led to the substitution by pagans of dies Solis for dies Saturni, as the first day of the planetary week. Thus gradually a pagan institution was engrafted on Christianity."

--Hutton Webster, Rest Days, pp. 220-221. [Webster (1875-?), was an author, historian, and professor at the University of Nebraska].

 

The text of Constantine's Sunday Law of 321 A.D. is :

"One the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed. In the country however persons engaged in agriculture may freely and lawfully continue their pursuits because it often happens that another day is not suitable for gain-sowing or vine planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost. (Given the 7th day of March, Crispus and Constantinebeing consuls each of them the second time."

Codex Justinianus, lib. 3, tit. 12, 3; translated in History of the Christian Church, Philip Schaff, D.D., (7-vol.ed.) Vol. III, p.380. New York, 1884

"Here is the first Sunday Law decree of a Christian council. It was given about 16 years after Constantine's first Sunday Law of A.D. 321: "Christians shall not Judaize and be idle on Saturday [in the original: "sabbato"--shall not be idle on the Sabbath], but shall work on that day; but the Lord's day they shall especially honour, and as being Christians, shall, if possible, do no work on that day. If, however, they are found Judaizing, they shall be shut out ['anathema,'--excommunicated] from Christ."

--Council of Laodicea, c. A.D. 337, Canon 29, quoted in C.J. Hefele, "A History of the Councils of the Church," Vol. 2, p. 316.

“Centuries of the Christian era passed away before the Sunday was observed by the Christian church as a Sabbath. History does not furnish us with a single proof or indication that it was at any time so observed previous to the Sabbatical edict of Constantine in A.D. 321.”

Examination of the Six Texts, p. 291. Sir Win. Domville —

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"Our observance of Sunday as the Lord's day is apparently derived from Mithraism. The argument that has sometimes been used against this claim, namely, that Sunday was chosen because of the resurrection on that day, is not well supported."

Gordon J. Laing, "Survivals of Roman Religion," p. 148.

From history, we may determine that Sunday sacredness was being spread by some 'tradtion' rather than scripture among “Christians” around the end of the second century, or 200 A. D. History tells us that it spread from Rome during the next few centuries until it had almost wholly replaced the seventh day Sabbath by the end of the fifth century, or 500 A. D.