So there are two ways the works of the devil are destroyed in this text. One is by the appearing of the Son of God and the other is by new birth. It's not enough for Jesus to come and die and rise again. People must be born of God. Otherwise the works of the devil are not destroyed.
Sin goes on reigning.
Nor is it possible that God should just cause people to be born anew without the appearance of the Son of God. Both are necessary. To answer this we need to see what it means to be born of God. Now anybody can sin who wants to sin. So when John says that a person born of God cannot sin, he must mean that a person born of God has new wants, new desires.