Sunday keeping
GE
I was not the one that brought in Acts 17.
Also, I am not quite sure what you are getting at regarding Col 2:18-19. To me these verses didn't really seem to be addressing those teaching keeping the law. It appears that some were into "angel worship" and voluntary humility (which was probably some form of asceticism) that Paul saw as taking away from Christ the same way the handwriting of ordinances did.
Also, I am not a Sundaydarian or Sabbatharian. I think both sides pushing(not practicing) their view are wrong. If you want to do either, do it unto the Lord without talking about it for a couple of years and see how you feel.
Romans 14:17 For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost. 18 For he that in these things(including the issue addressed in vv. 5-6) serveth Christ is acceptable to God, and approved of men. 19 Let us therefore follow after the things which make for peace, and things wherewith one may edify another.
It is sad that some unbelievers may visit this site and ask "why dost thou set at nought thy brother? (V. 10) instead of saying look at them edify each other(v 19).:tear: I say this as somebody that was guilty of judging my brother regarding this issue and saw the "fruit" it bore.
Acts 17 and 20 do not seem to provide a lot of support for making a doctrine which clearly contradicts the truths in Romans 14. They did these things. Does that mean we need to? Ever do a holy kiss, have your wife wear a headcovering, refuse to eat some meats...? Look at some modern examples - dividng based on music styles, clothes, modes of education,... God is saddened by it all.
So my answer to the question "Why does the Sunday-keeping church think of Sunday as the Sabbath?" is that they think the early church did it so we should to. Paul would say:
16 Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days: 17 Which are a shadow of things to come; but the body is of Christ. 18 Let no man beguile you of your reward in a voluntary humility and worshipping of angels, intruding into those things which he hath not seen,
vainly puffed up by his fleshly mind, 19 And not holding the Head, from which all the body by joints and bands having nourishment ministered, and knit together, increaseth with the increase of God.
20 Wherefore if ye be dead with Christ from the rudiments of the world, why, as though living in the world, are ye subject to ordinances, 21 (Touch not; taste not; handle not; 22 Which all are to perish with the using

after the commandments and doctrines of men? 23 Which things have indeed a shew of wisdom in will worship, and humility, and neglecting of the body: not in any honour to the satisfying of the flesh.
There, I didn't leave them out this time! :thumbs:
Thanks for asking. God bless!