The New Covenant
Christians today are not under the law God gave to Israel at Mt Sinai. While this law (covenant) was in effect, Jeremiah, the prophet, foretold the Lord would make a new covenant with His people (Jeremiah 31:31-34). This was fulfilled when the New Testament was given (Hebrews 8:6-13). We today do not live under the law God gave to Israel. We live under the Law of Christ. Jesus Christ is our High Priest (Hebrews 4:14-16). “For the priesthood being changed, there is made of necessity a change also of the law” (Hebrews 7:12). That Old Law, which was given to Israel at Mt. Sinai, ceased when Jesus died on the cross: “having blotted out the bond written in ordinances that was against us, which was contrary to us: and he hath taken it out that way, nailing it to the cross” (Colossians 2:14; please see also Galatians, chapter 3 and 4 and II Corinthians, chapter 3).
Jesus Christ was born under the Law of Moses. He kept it perfectly. That is why He worshipped in the synagogue and the temple. The apostles often went into the synagogues to teach because the Jews gathered there were waiting for the Christ. But the apostles were not observing the Sabbath as a special day of worship. They were simply using it as an opportunity to teach the gospel!
The Bible plainly teaches the special day of worship for Christians is the first day of the week. This was being practiced in the days of the apostles as we have clearly shown. The claim made be the Seventh Day Adventists that Constantine changed the day of worship from Saturday to Sunday is false! Constantine simply made Sunday a legal day of rest from work because that was the day the Christians met in order to worship God.
Churches which select Saturday as a day of worship are in error, and they are wrong to require Sabbath keeping. True followers of Jesus Christ worship on the day He has authorized, which is Sunday, the first day of the week!