Why do I need to do what Jesus has already done. Jesus is God and Lord of the Sabbath.
As a follower of Jesus, I hark to His new covenant, and to the Day of the lord, the Lord’s day, Domenica.
Jesus said to keep His commandments of loving God and loving one’s fellow man
No reason. You can carry on lying, murdering and fornicating. He fulfilled the Law so you're good to go.
As a follower of Jesus
A follower of Jesus would follow His example of living. Including keeping the Sabbath. This weeds out the posers.
Jesus said to keep His commandments of loving God and loving one’s fellow man.
The Ten Commandments hinges on those two principles.