Adam Clarke's Commentary on the Bible

Verse 8 (1 John 3:8)

He that committeth sin is of the devil - Hear this, also, ye who plead for Baal, and cannot bear the thought of that doctrine that states believers are to be saved from all sin in this life! He who committeth sin is a child of the devil, and shows that he has still the nature of the devil in him; for the devil sinneth from the beginning - he was the father of sin, brought sin into the world, and maintains sin in the world by living in the hearts of his own children, and thus leading them to transgression; and persuading others that they cannot be saved from their sins in this life, that he may secure a continual residence in their heart. He knows that if he has a place there throughout life, he will probably have it at death; and, if so, throughout eternity.

For this purpose - Εις τουτο· For this very end - with this very design, was Jesus manifested in the flesh, that he might destroy, ἱνα λυσῃ , that he might loose, the bonds of sin, and dissolve the power, influence, and connection of sin. See on 1 John 3:3 ; (note).

- Adam Clarke's Commentary on the Bible