While Jesus lived on earth, He kept the Law of Moses and taught others to do so. In the Sermon on the Mount, Jesus said: "Think not that I am come to destroy the law, or the prophets; I am not come to destroy, but to fulfill. For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled (Matthew 5:17,18). Please notice that Jesus said nothing would pass from the Law "till all be fulfilled."
Jesus fulfilled all that was written in the Old Testament--the Law, the Psalms, and the Prophets. "And He said unto them, These are the words which I spoke unto you, while I was yet with you, that all things must be fulfilled, which were written in the Law of Moses, and in the prophets, and in the psalms concerning me" (Luke 24:44).
The purpose of the Law which was given to Israel at Mt. Sinai, the Law of Moses, is clearly seen in the book of Galatians. "Wherefore then serveth the Law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator" (Galatians 3:19). The Law was to be in effect "till the seed should come." The promised seed was Jesus Christ (Genesis 3:15; 12:1-3; Galatians 3:16).
Please notice again, "Wherefore the Law was our schoolmaster to bring us unto Christ, that we might be justified by faith. But after faith is come, we are no longer under a schoolmaster"(Galatians 3:24,25). If we are no longer under the Law of Moses, then obviously the Sabbath law is not binding upon us today.
When did the Law of Moses as a law binding upon God’s people end? The answer is, it ended when Jesus died on the cross thus fulfilling it. Please notice: "But now in Christ Jesus ye who sometime were far off are made nigh by the blood of Christ. For He is our peace, who hath made both one, and hath broken down the middle wall of partition between us: Having abolished in His flesh the enmity, even the law of commandments contained in ordinances; for to make in Himself of twain one new man, so making peace" (Ephesians 2:13-15). Jesus abolished the law of commandments (the Law of Moses which included the command to keep the sabbath, Exodus 20:8). He abolished it "in His flesh;" that is by His death on the cross (cf. Colossians 2:14-17).
The new law, the Law of Christ, came into effect on Pentecost Day (Acts 2). On that day, the church of Christ was established (Acts 2:36-47). From that time, we find Christians meeting to worship upon the first day of the week which is Sunday. "Upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight" (Acts 20:7). "Now concerning the collection for the saints, as I have given order to the churches of Galatia, even so do ye. Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come" (I Corinthians 16:1,2).
In summary, why do Christians meet for worship upon Sunday,
the first day of the week, instead of Saturday, the seventh day of the
week? The teaching of the Bible is plain. The Law of Moses, which included
the sabbath commandment, was to the nation of Israel only. It lasted as
a binding law until Christ died on the cross. The Law of Christ, which
began at Pentecost, is God’s law for all mankind today. The Law of Christ
teaches that we are to meet on Sunday, the first day of the week. This
is the day upon which our Lord arose from the dead (Matthew 28:1; Mark
16:2-6; Luke 24:1; John 20:1). The day upon which the church began, Pentecost
day, also was on the first day of the week (Leviticus 23:9-16). Therefore,
we can see why the Lord chose the first day of the week as the day of worship
for Christians.