Growing distinction from the Sabbath
23. It was this newness which the catechesis of the first centuries stressed as it sought to show the prominence of Sunday relative to the Jewish Sabbath. It was on the Sabbath that the Jewish people had to gather in the synagogue and to rest in the way prescribed by the Law. The Apostles, and in particular Saint Paul, continued initially to attend the synagogue so that there they might proclaim Jesus Christ, commenting upon "the words of the prophets which are read every Sabbath" (Acts 13:27). Some communities observed the Sabbath while also celebrating Sunday. Soon, however, the two days began to be distinguished ever more clearly, in reaction chiefly to the insistence of those Christians whose origins in Judaism made them inclined to maintain the obligation of the old Law.
Saint Ignatius of Antioch writes: "If those who were living in the former state of things have come to a new hope, no longer observing the Sabbath but keeping the Lord's Day, the day on which our life has appeared through him and his death ..., that mystery from which we have received our faith and in which we persevere in order to be judged disciples of Christ, our only Master, how could we then live without him, given that the prophets too, as his disciples in the Spirit, awaited him as master?".(21) Saint Augustine notes in turn: "Therefore the Lord too has placed his seal on his day, which is the third after the Passion. In the weekly cycle, however, it is the eighth day after the seventh, that is after the Sabbath, and the first day of the week".(22) The distinction of Sunday from the Jewish Sabbath grew ever stronger in the mind of the Church, even though there have been times in history when, because the obligation of Sunday rest was so emphasized, the Lord's Day tended to become more like the Sabbath. Moreover, there have always been groups within Christianity which observe both the Sabbath and Sunday as "two brother days".(23)