Why do most Christians celebrate on Sunday? Because Christ gave us something much better.....a new covenant, which is much better than the old and which fulfilled the Jewish Sabbath.
Does that mean the other nine commandments are not relevant?
Christ gave us a much better law. He said that the two greatest commandments is to love God with all your heart, mind, and soul, and secondly to love your neighbor as yourself. These two fulfill all the laws and the prophets.
This "six day" creation was linked to the Sabbath because the Sabbath has something to do with mankind's salvation.
Not once does the scripture imply keeping the Sabbath is crucial to our salvation.
Yes, it does. The Holy Bible says that God commanded Israel to keep the Sabbath. Not keeping the Sabbath would be going against what God commanded. It is called "disobedience." Disobedience to God or going against God's commandment will not bring you salvation.
Finally, the Sabbath of the Christians is not the same as the Jews. For Christians, they are no longer under the Old Covenant. They are now under the New Covenant. This New Covenant brought fourth a new Sabbath for Christians, which is Sunday.....the Lord's Day. It was on Sunday when Christ rose from the dead. It was on Sunday when Christ ascended to Heaven. It was Sunday when the Holy Spirit descended on the Apostles and His disciples, and it was on Sunday when the Apostles "broke bread" with each other. Sunday became known as the Lord's Day.....and Sunday was linked to a NEW CREATION. It was in Christ Jesus that Christians were made into a new creation and we became a new creature in Christ's death and resurrection.
This is all fanciful speculation that is not backed up by scripture.
Actually, it is found in Scripture.
1. God DID create a new convenant (See Jeremiah 31:31, Hebrews 8:8, Hebrews 9:15, Hebrews 12:24). Therefore we are under a new convenant, and the Mediator of the New Covenant is Jesus (See Hebrews 12:24). Already in the Old Testament, God expressed disappointment over the Hebrew Sabbath (See Isaiah 1:13-15).
2. It was on Sunday when Christ rose from the dead (See Matthew chapter 28).
3. The Holy Spirit descended upon the Church on Pentecost Sunday (See Acts 2:1-3).
4. After His Resurrection, Jesus appeared to the Apostles twice, each on Sunday (See John 20:19 & 26).
5. It was also on Sundays that the Apostles assembled together to break bread (See Acts 20:7).
6. The Holy Bible does speak of the Lord's Day. It was on Sunday when St. John received a revelation from God and wrote the Book of Revelation (Rev. 1:10). St. John stated that he was in the spirit on the Lord's Day. The Lord's Day is Sunday.
Sunday fulfills the spiritual truth of the Jewish Sabbath and announces man's eternal rest in God.
Where does it say this in scripture?
Jesus is the end of the law and the Lord of the Sabbath (See Romans 10:4 and Mark 2:28) Jesus Christ is the blood of the New Covenant shed for our sins (See Mark 14:24). Christ is the Mediator of the New Covenant (See Hebrews 12:24). Why should I follow the Old Covenant when I should be following Jesus, our Mediator of the New Covenant?
Sunday fulfills the spiritual truth of the Jewish Sabbath because it is only in Jesus (the Mediator of the New Covenant) where one can find eternal rest in God. It is NOT the Jewish Law or the Jewish Sabbath that will give us eternal life and eternal rest, but Christ Himself, who is the end of the Law and the Lord of the Sabbath. His resurrection (which occurred on a Sunday) is what gave us redemption and salvation. We are no longer under the Old Covenant. We are under the New Covenant because our Lord Jesus Christ is the Mediator of that New Covenant (See Hebrews 12:24).