4 But nevertheless you are bidden to say, with arm outstretched towards him as though he were present, “I renounce you, Satan.” I wish also to say wherefore ye stand facing to the West; for it is necessary. Since the West is the region of sensible darkness, and he being darkness has his dominion also in darkness, therefore, looking with a symbolic meaning towards the West, you renounce that dark and gloomy potentate. What then did each of you stand up and say? “I renounce you, Satan,”— you wicked and most cruel tyrant! Meaning, “I fear your might no longer; for that Christ has overthrown, having partaken with me of flesh and blood, that through these He might by death destroy death, that I might not be made subject to bondage for ever.” “I renounce you,”— you crafty and most subtle serpent. “I renounce you,”— plotter as you are, who under the guise of friendship contrived all disobedience, and work apostasy in our first parents. “I renounce you, Satan,”— the artificer and abettor of all wickedness.
Source: Catechetical Lectures (New Advent)