CCC 2852 “A murderer from the beginning,. .. a liar and the father of lies,” Satan is “the deceiver of the whole world.”¹ Through him sin and death entered the world and by his definitive defeat all creation will be “freed from the corruption of sin and death.”² Now “we know that anyone born of God does not sin, but He who was born of God keeps him, and the evil one does not touch him. We know that we are of God, and the whole world is in the power of the evil one.”³
The Lord who has taken away your sin and pardoned your faults also protects you and keeps you from the wiles of your adversary the devil, so that the enemy, who is accustomed to leading into sin, may not surprise you. One who entrusts himself to God does not dread the devil. “If God is for us, who is against us?”⁴

1 Jn 8:44; Rev 12:9.
2 Roman Missal, Eucharistic Prayer IV, 125.
3 1 Jn 5:18-19.
4 St. Ambrose, De Sacr. 5, 4, 30: PL 16, 454; cf. Rom 8:31.