Q. How early in Church history was Mass celebrated on Sundays?
A. The early Christians began meeting for worship on Sundays (the first day of the week) instead of Saturdays (the seventh day, the “Sabbath,” as prescribed in the Law of Moses) because that was the day on which Jesus rose from the dead. They called it “the Lord’s Day.” Some denominations that insist on Saturday Sabbath worship claim that this change took place after the Roman Emperor Constantine meddled in Church affairs in the fourth century. But Scripture and several early Christian writers provide sufficient evidence to the contrary.
In Scripture, St. Paul says the first believers came together on the first day of the week (1 Corinthians 16:2), as does the Book of Acts (20:7). The latter notes that it’s the day on which believers came to “break bread,” which was how the early Christians described the Eucharist. The Book of Revelation also refers to “the Lord’s Day” (Revelation 1:10).
As for other ancient witnesses to Sunday worship, St. Ignatius of Antioch wrote soon after the composition of St. John’s Gospel (sometime before the year 117): “We are no longer keeping the [seventh-day] Sabbath, but the Lord’s Day” (Epistle to the Magnesians, 9, 1).
The early Christian theologian named Origen reported in the late 100s: “The Word [Christ] has moved the feast of the Sabbath to the day on which the light was produced and has given us as an image of true repose, Sunday, the day of salvation, the first day of the light in which the Savior of the world, after completing all his work with men and after conquering death, crossed the threshold of heaven, surpassing the creation of the six days and receiving the blessed Sabbath and rest in God” (Commentary on Psalm 91).