Whosoever abideth in him - By faith, love, and obedience.

Sinneth not - Because his heart is purified by faith, and he is a worker together with God, and consequently does not receive the grace of God in vain. See on 1 John 3:3 (note).

Hath not seen him - It is no unusual thing with this apostle, both in his gospel and in his epistles, to put occasionally the past for the present, and the present for the past tense. It is very likely that here he puts, after the manner of the Hebrew, the preterite for the present: He who sins against God doth not see him, neither doth he know him - the eye of his faith is darkened, so that he cannot see him as he formerly did; and he has no longer the experimental knowledge of God as his Father and portion.

abideth.

1 John 2:28 And now, little children, abide in him; that, when he shall appear, we may have confidence...

John 15:4-7 Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can you...

whosoever.

1 John 3:2,9 Beloved, now are we the sons of God, and it does not yet appear what we shall be: but we know that, when he shall appear...

1 John 2:4 He that said, I know him, and keeps not his commandments, is a liar, and the truth is not in him.

1 John 4:8 He that loves not knows not God; for God is love.

1 John 5:18 We know that whoever is born of God sins not; but he that is begotten of God keeps himself, and that wicked one touches him not.

2 Corinthians 3:18 But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory...

2 Corinthians 4:6 For God, who commanded the light to shine out of darkness, has shined in our hearts...

3 John 1:11 Beloved, follow not that which is evil, but that which is good. He that does good is of God: but he that does evil has not seen God.

The Love that Calls us Sons
'Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God....'--1 John iii. 1. One or two points of an expository character will serve to introduce what else I have to say on these words. The text is, I suppose, generally understood as if it pointed to the fact that we are called the sons of God as the great exemplification of the wonderfulness of His love. That is a perfectly possible view of the connection and meaning of the text. But if we are to …
Alexander Maclaren—Expositions of Holy Scripture Ephesians, Peter,John

The End of Christ's Coming
"For this purpose was the Son of God manifested, that he might destroy the works of the devil." 1 John 3:8. 1. Many eminent writers, heathen as well as Christian, both in earlier and later ages, have employed their utmost labour and art in painting the beauty of virtue. And the same pains they have taken to describe, in the liveliest colours, the deformity of vice; both of vice in general, and of those particular vices which were most prevalent in their respective ages and countries. With equal care …
John Wesley—Sermons on Several Occasions

The Great Privilege of those that are Born of God
"Whosoever is born of God doth not commit sin." 1 John 3:9. 1. It has been frequently supposed, that the being born of God was all one with the being justified; that the new birth and justification were only different expressions, denoting the same thing: It being certain, on the one hand, that whoever is justified is also born of God; and, on the other, that whoever is born of God is also justified; yea, that both these gifts of God are given to every believer in one and the same moment. In one …
John Wesley—Sermons on Several Occasions