Some people object to the traditional Christian practice of gathering on Sunday as a community to worship God, believing that Saturday is the day Christians are supposed to gather. Among those who hold these objections to the traditional Christian practice are the Seventh Day Adventists, who are relatively prominent in our area.
Arguments in favor of worship on Saturday sound fairly convincing at first glance. Those who believe in Saturday worship cite the fact that the Jewish Sabbath day was on Saturday, which is certainly true. They also point out that Jesus kept the Sabbath, which is also mostly true. But neither of these reasons are why Christians began to worship on Sunday.
The reason the early Christians worship on Sunday was because Jesus rose from the dead on a Sunday, which was now known as the Lord’s day. Early on Christians saw Sunday as “The eighth Day,” signaling a new age of existence. In fact, Jewish converts to Christianity began keeping the Sabbath and the Lord’s day. Gentile Christians never really kept the Sabbath as Jewish people understood it, but met on the Lord’s day only where they heard preaching and “broke bread.”
That “The Lord’s Day” was Sunday and that the Lord’s day was the day Christians met is clear from the writings of early Christians. The Didache is the earliest Christian non-biblical text we have. Written in the year 70 A.D, It clearly shows that “The Lord’s Day” is the day Christians gathered. It states, “"But every Lord’s day . . . gather yourselves together and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure.”
Another early document, The Letter of Barnabas, is also clear. Written in the year 74, it says, “"We keep the eighth day [Sunday] with joyfulness, the day also on which Jesus rose again from the dead.” Ignatius of Antioch, writing in 110 said, “[T]hose who were brought up in the ancient order of things [i.e. Jews] have come to the possession of a new hope, no longer observing the Sabbath, but living in the observance of the Lord’s day, on which also our life has sprung up again by him and by his death."
Finally, in the year 155 Justin Martyr wrote, "But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Savior on the same day rose from the dead."
On the other hand, we do not see any such writings from the early Church clearly stating that Christians gathered together to celebrate the Resurrection on Saturday. That is very telling. Worshipping on Sunday was not even seriously questioned until relatively recent times. The most dominant religious group claiming that God intends us to worship on Saturdays is the Seventh Day Adventist Church which did not even begin until 1863.
This is not intended to be a thorough defense of Sunday worship, and I encourage you to look into this issue more deeply on your own. For more on this topic, I encourage you to see Sabbath or Sunday on the Catholic Answers website. Also on the Catholic Answers website you can find some information on Seventh Day Adventism and its history of anti-Catholicism in the tract, Seventh Day Adventism. There are also some great testimonies from some Catholic Converts from Seventh Day Adventism who had to examine this issue personally, which you can find at the Coming Home Network.