We all gather on the day of the sun, for it is the first day [after the Jewish sabbath, but also the first day] when God, separating matter from darkness, made the world; and on this same day Jesus Christ our Savior rose from the dead. 106
Catechism number 2175
Sunday is expressly distinguished from the sabbath which it follows chronologically every week; for Christians its ceremonial observance replaces that of the sabbath. In Christ's Passover, Sunday fulfills the spiritual truth of the Jewish sabbath and announces man's eternal rest in God. For worship under the Law prepared for the mystery of Christ, and what was done there prefigured some aspects of Christ:107