The first day of the week. Since New Testament times it replaced the Jewish Sabbath (Acts 20:7; I Corinthians 16:2). St. John called it the Lord's Day, which the Western Church later translated Dominica. The immediate reason for substituting Sunday for the Sabbath was to commemorate Christ's Resurrection from the dead. Eventually sunday also became a memorial of the descent of the Holy Spirit on Pentecost. MOreover, the original purpose of the Sabbath remained as a liturgical day of rest to recall God's lordship of the universe. "On the seventh day, He rested; that is why Yahweh has blessed the sabbath day and made it sacred" (Exodus 20;8-11).