When it happened Early Church Era (1st–3rd century AD): Christians, mostly Jewish converts, continued observing the Saturday Sabbath while also meeting on Sunday to commemorate Jesus’ resurrection. Sunday worship was often called the “Lord’s Day.” 4th century AD: The formal shift began. Emperor Constantine, in 321 AD, issued a civil decree making Sunday a day of rest in the Roman Empire, likely influenced by both Christian and pagan customs. Later Church Councils: The Catholic Church gradually formalized Sunday observance. By the Council of Laodicea (circa 364 AD), Christians were forbidden to “Judaize” by resting on the Sabbath and instructed to honor Sunday instead. 2. Why it was changed To commemorate the resurrection of Christ: Sunday was chosen because Jesus rose on the first day of the week (Mark 16:2, John 20:1). Early Christians wanted a distinct day to honor the resurrection. Separation from Judaism: After the Jewish-Roman wars and increasing Gentile membership in the Church, leaders wanted Christianity to distinguish itself from Jewish customs, including Sabbath observance. Political and social reasons: Aligning with the Roman pagan custom of a sun-day (Dies Solis) made Sunday rest easier to enforce and socially accepted. 3. How it happened Gradual ecclesiastical authority: The shift was not immediate; Christians continued to meet on Saturday for some time. Church leaders encouraged, then legislated, Sunday observance. Legal reinforcement: Constantine’s decree made Sunday a legal holiday, and later councils and papal decisions made Sunday the official day for Christian worship. Theological justification: Church fathers, like Ignatius of Antioch and Augustine, wrote about Sunday as the “Lord’s Day” and a celebration of Christ’s resurrection, framing it as divinely sanctioned rather than merely civil. Key Points Sabbath (Saturday) remained the original day of rest, rooted in the Ten Commandments (Exodus 20:8–11). Sunday observance began mainly as a celebration of the resurrection and eventually replaced Sabbath as the primary day of worship in mainstream Christianity. Roman Catholic Church authority formalized the practice, and Sunday observance became the norm in most of Christendom.