The New Testament makes it clear that the earliest Christians already worshiped on Sunday in commemoration of the resurrection of their Savior (Acts 20:7). The book of Acts highlights the tension between Greek-speaking Jews and Aramaic-speaking Jews in Jerusalem and between Jewish Christians who wanted to retain outward signs of their “Jewishness” (kosher food, Sabbath and festivals observance) and Gentile Christians who had no interest in such things.
Paul’s approach to the conflict was to emphasize unity in Christ and to call for Christian liberty in non-essentials:
For though I am free from all men, I have made myself a servant to all, that I might win the more; and to the Jews I became as a Jew, that I might win Jews; to those who are under the law, as under the law, that I might win those who are under the law; to those who are without law, as without law (not being without law toward God, but under law toward Christ), that I might win those who are without law; to the weak I became as weak, that I might win the weak. I have become all things to all men, that I might by all means save some. Now this I do for the gospel’s sake, that I may be partaker of it with you (1 Corinthians 9:19-23 NKJV).
As hostility towards Jewish Christians grew within Judaism itself, it became more and more difficult for culturally Jewish Christians to continue to participate in Jewish religious practices.
After the First Jewish-Roman War, Jewish leaders inserted an anti-Christian curse in the prayer that was recited at every gathering for synagogue worship, making it impossible for Jews who were Christians to participate. They also established a canon, or official list, of books they considered authoritative, rejecting early Christian books that were in circulation and abandoning the Septuagint, in spite of its prestige and widespread use. (The Septuagint was popular with Christians, and its translations of key prophetic passages corroborated Christian beliefs.)
After the national repudiation of Jesus Christ and the gospel, Judaism fell under the control of the kind of Pharisaism that was most violently opposed to Jesus. During the next four centuries, the “traditions of the elders” were systematized, codified, and amplified in the Talmud, which contained some virulently anti-Christian passages.
Once Judaism defined itself by rejection of Jesus Christ, it was impossible for Jewish Christians to remain culturally Jewish, and Sabbath-observance virtually ceased.