The thing is the Lord actually declared that the law and prophets are actually the golden rule ( Matthew 7:12). The Lord said that His great commandments are on which the law & prophets depend ( Matthew 22:36-40). Jesus Christ told the rich young man the same commandments ( Matthew 19:16-19) that St. Paul preached to us ( Romans 13:8-10.
The Apostles held council and gave St. Paul etc. the basic instructions per Acts 15:22-31. There is no emphasis on the Saturday sabbath in any of this although it seems to be permitted. The Messianic Jewish community was severely weakened when St. James was martyred ( Acts 12:1-5).
When reading the most ancient, few surviving church accounts, Sunday ( per Matthew 28:9) is clearly the “Lord’s Day”. In Acts 20:7-11, the pattern of Sunday worship was developing. Compare the scripture to this quote from the Didache manual from about 100 AD:
14:1 And on the Lord's own day gather yourselves together and break bread and give thanks, first confessing your transgressions, that your sacrifice may be pure.
Didache. The Teaching of the Twelve Apostles (translation J. B. Lightfoot). On Early Christian Writings.
www.earlychristianwritings.com
The ancient church communities did not recklessly, or in hostility, spitefully etc. discontinue the Saturday sabbath. Nonetheless the old sabbath was discontinued from early on in most places.