Christians replaced the celebration of the Sabbath with the celebration of Sunday because Jesus Christ rose from the dead on a Sunday. The “Lord’s Day”, however, does include elements of the Sabbath.
The Christian Sunday has three essential elements: (1) it recalls the creation of the world and communicates the festive splendour of God’s goodness to the passage of time. (2) It recalls the “eighth day of creation”, when the world was made new in Christ (thus a prayer from the Easter Vigil says: “You have wonderfully created man and even more wonderfully restored him.”). (3) It includes the theme of rest, not just to sanctify the interruption of work, but to point even now toward man’s eternal rest in God.
(From the Catholic Youth Catechism question 364)