What must one do to be saved?
Repentance(ask for forgiveness for sins)
Belief/faith(real enduring faith and trust)
Not Baptism(this is a symbol of spiritual renewal)Romans 6, 1 Corinthians 1

The early Church has no Sabbath
Christians would go to synagogues on saturday to try to convert other Jews to believe Jesus was the Messiah
Colossians 2:16,17 do not need to observe Kosher Laws, no sabbath, festivals, Romans 14:5

God never intended for humans to follow the Law, Paul believed the Lord created the Law this way so people would mess up and realize how awful they were, then get down on their knees to ask for mercy and forgiveness.
Paul on the Law, Paul says three things: tutor to lead us to Christ(teaches us how bad we are), Curse from which Christ saved us, Testraint on sin(before the Holy Spirit)
Galatians)

You don't need to follow the Law to be a Christian, but you need to still follow the moral aspects of the Law. just no ceremonies, or dietary law or rituals.