I believe the church began in seed form with the earthly ministry of Jesus Christ. There was a transition period from Jesus' earthly ministry all the way until A.D. 70 in which the Old Covenant was being faded out and the New Covenant was brought in with the resurrection of Christ.
Dan 9:27 And he [Messiah] shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease...
Jesus confirmed/strengthened the covenant with Old Covenant Israel (the natural branches) for one week (seven years).
Joh 4:22 Ye worship ye know not what: we know what we worship: for salvation is of the Jews.
Joh 4:23 But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him.
Mat 15:24 But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
Mat 15:25 Then came she and worshipped him, saying, Lord, help me.
Mat 15:26 But he answered and said, It is not meet to take the children's bread, and to cast it to dogs.
Mat 15:27 And she said, Truth, Lord: yet the dogs eat of the crumbs which fall from their masters' table.
Mat 15:28 Then Jesus answered and said unto her, O woman, great is thy faith: be it unto thee even as thou wilt. And her daughter was made whole from that very hour.
Mat 10:5 These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not:
Mat 10:6 But go rather to the lost sheep of the house of Israel.
However, during this focus on Israel and confirming "the covenant" including enforcing the Law before the atonement, Christ prepared His converts to embrace the New Covenant.
Mat 9:17 Neither do men put new wine into old bottles: else the bottles break, and the wine runneth out, and the bottles perish: but they put new wine into new bottles, and both are preserved.
Joh 3:5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
Joh 3:6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
Joh 5:23 That all men should honour the Son, even as they honour the Father. He that honoureth not the Son honoureth not the Father which hath sent him.
Joh 5:24 Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life.
Joh 5:25 Verily, verily, I say unto you, The hour is coming, and now is, when the dead shall hear the voice of the Son of God: and they that hear shall live.
In the "midst of the week" (after 3 1/2 years of ministry) He was "cut off" and He "caused the sacrifice and oblation to cease" by His ultimate sacrifice on the Cross.
Heb 10:5 Wherefore when he cometh into the world, he saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me:
What about the remaining 3 1/2 years? I believe it was 3 1/2 years until the conversion of Cornelius and the Apostle Paul when "the covenant" with natural Israel ended and the Gentiles were given the word of the gospel. The definition of Israel changed from the Old Covenant to the New Covenant.
The Old Covenant was a geopolitical covenant of earthly descent and a community comprising regenerates and unregenerates. The primary sign of the covenant--circumcision--was propagated at physical birth and pointed toward a future faith.
The New Covenant is a perfect covenant of spiritual rebirth and is an invisible covenant of regenerates only in which "all shall know Me from the least to the greatest." The primary sign of the covenant--baptism--is (supposed to be) propagated at spiritual birth and points back at existing faith.
Rom 11:5 Even so then at this present time also there is a remnant according to the election of grace.
Rom 11:6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.
Rom 11:7 What then? Israel hath not obtained that which he seeketh for; but the election hath obtained it, and the rest were blinded
Jer 11:1 The word that came to Jeremiah from the LORD, saying,
Jer 11:2 Hear ye the words of this covenant, and speak unto the men of Judah, and to the inhabitants of Jerusalem;
Jer 11:3 And say thou unto them, Thus saith the LORD God of Israel; Cursed be the man that obeyeth not the words of this covenant,
Jer 11:16 The LORD called thy name [Israel], A green olive tree, fair, and of goodly fruit: with the noise of a great tumult he hath kindled fire upon it, and the branches of it are broken.
Jer 11:17 For the LORD of hosts, that planted thee, hath pronounced evil against thee, for the evil of the house of Israel and of the house of Judah, which they have done against themselves to provoke me to anger in offering incense unto Baal.
Rom 11:17 And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in AMONG THEM, and with them partakest of the root and fatness of the olive tree;
Under the Old Covenant the unbelievers stayed in the natural olive tree and wilted off. When The New Covenant was enforced and the "covenant" with Israel was finished being confirmed, the unbelieving natural branches were cut off from the olive tree of true Israel and hardened in blindness. God then grafted the wild branches of the believing Gentiles into this olive tree. The resulting "Israel" under the auspices of the New Covenant is a tree in which all members are believers.
Heb 8:6 But now hath he obtained a more excellent ministry, by how much also he is the mediator of a better covenant, which was established upon better promises.
Heb 8:7 For if that first covenant had been faultless, then should no place have been sought for the second.
Heb 8:8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
Heb 8:9 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord.
Heb 8:10 For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
Heb 8:11 And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest.
Heb 8:12 For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
Heb 8:13 In that he saith, A new covenant, he hath made the first old[/b]. Now that which decayeth and waxeth old is ready to vanish away.
Indeed, the old was ready to vanish away. The book of Hebrews was written to Jewish Christians from the perspective of the Old Covenant composition to escape to the New Covenant. The Old Covenant was put away in its entirety upon the destruction of Jerusalem in A.D. 70.