Mark 2:27-28
27 And He said to them, "The Sabbath was made for man, and not man for the Sabbath. 28 Therefore the Son of Man is also Lord of the Sabbath." NKJV
Galatians 3:23-25
24 Therefore the law was our tutor to bring us to Christ, that we might be justified by faith. 25 But after faith has come, we are no longer under a tutor. NKJV
James 2:8-13
8 If you really fulfill the royal law according to the Scripture, "You shall love your neighbor as yourself," you do well; 9 but if you show partiality, you commit sin, and are convicted by the law as transgressors. 10 For whoever shall keep the whole law, and yet stumble in one point, he is guilty of all. 11 For He who said, "Do not commit adultery," also said, "Do not murder." Now if you do not commit adultery, but you do murder, you have become a transgressor of the law. 12 So speak and so do as those who will be judged by the law of liberty. 13 For judgment is without mercy to the one who has shown no mercy. Mercy triumphs over judgment. NKJV
Hebrews 7:12-17
12 For the priesthood being changed, of necessity there is also a change of the law. 13 For He of whom these things are spoken belongs to another tribe, from which no man has officiated at the altar.
14 For it is evident that our Lord arose from Judah, of which tribe Moses spoke nothing concerning priesthood. 15 And it is yet far more evident if, in the likeness of Melchizedek, there arises another priest 16 who has come, not according to the law of a fleshly commandment, but according to the power of an endless life. 17 For He testifies:
"You are a priest forever
According to the order of Melchizedek." NKJV
God blessed the seventh day as a day of rest in Genesis 2, which is made clear in:
Exodus 20:8-11
8 "Remember the Sabbath day, to keep it holy. 9 Six days you shall labor and do all your work, 10 but the seventh day is the Sabbath of the LORD your God. In it you shall do no work: you, nor your son, nor your daughter, nor your male servant, nor your female servant, nor your cattle, nor your stranger who is within your gates. 11 For in six days the LORD made the heavens and the earth, the sea, and all that is in them, and rested the seventh day. Therefore the LORD blessed the Sabbath day and hallowed it. NKJV
Deuteronomy 5:12-15
12'Observe the Sabbath day, to keep it holy, as the LORD your God commanded you. 13 Six days you shall labor and do all your work, 14 but the seventh day is the Sabbath of the LORD your God. In it you shall do no work: you, nor your son, nor your daughter, nor your male servant, nor your female servant, nor your ox, nor your donkey, nor any of your cattle, nor your stranger who is within your gates, that your male servant and your female servant may rest as well as you. 15 And remember that you were a slave in the land of Egypt, and the LORD your God brought you out from there by a mighty hand and by an outstretched arm; therefore the LORD your God commanded you to keep the Sabbath day.
NKJV
For the Israelites the Sabbath become a day of worship or a "holy convocation" in Levititcus:
Leviticus 23:3
'Six days shall work be done, but the seventh day is a Sabbath of solemn rest, a holy convocation. You shall do no work on it; it is the Sabbath of the LORD in all your dwellings. NKJV
There is Biblical evidence that the church met on the first day of the week:
Acts 20:7
Now on the first day of the week, when the disciples came together to break bread, Paul, ready to depart the next day, spoke to them and continued his message until midnight.
NKJV
1 st Corinthians 16:1-2
Now concerning the collection for the saints, as I have given orders to the churches of Galatia, so you must do also: 2 On the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come.
NKJV
Also Paul wrote:
Colossians 2:16-17
16 So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, 17 which are a shadow of things to come, but the substance is of Christ. NKJV
What I find interesting about those who insist on the Sabbath as the only acceptable day of worship or as a holy convocation is these same people do not insist that all holy convocations are to be observed today.
Holy convocations under the law:
Passover: (Leviticus 23:4-8, Numbers 23:16-25)
1st and 7th day of the Feast of Unleavened Bread: (Leviticus 23:4-8, Numbers 23:16-25)
Feast of Weeks: (Leviticus 23:15-22, Number 28:26-31)
Feast of Trumpets: (Leviticus 23:23-25, Numbers 29:1-6)
Day of Atonement: (Leviticus 23:26-32, Numbers 29:7-11)
Feast of Tabernacles: (Leviticus 23:33-36, Numbers 29:12-40)