Albert Barnes Commentary 1 John 3:24

"And he that keepeth his commandments abideth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he gave us." — 1 John 3:24 (ASV)

And he that keepeth his commandments, etc. (John 14:23).

And hereby we know that he abideth in us. That is, this is another certain evidence that we are true Christians. The Savior had promised (John 14:23) that He would come and take up His abode with His people. John says that we have proof that He does this by the Spirit He has given us.

That is, the Holy Spirit is imparted to His people to enlighten their minds; to elevate their affections; to sustain them in times of trial; to quicken them in the performance of duty; and to imbue them with the temper and spirit of the Lord Jesus. When these effects exist, we may be certain that the Spirit of God is with us, for these are the fruits of that Spirit, or these are the effects which He produces in the lives of men. .

On the evidence of piety referred to here, see Romans 8:9, Romans 8:14, and Romans 8:16.

No one can be a true Christian in whom that Spirit does not constantly dwell, or to whom He is not given. And yet no one can determine that the Spirit dwells in him, except by the effects produced in his heart and life. In the following chapter, the apostle pursues the subject suggested here and shows that we should examine ourselves closely, to see whether the Spirit to which we trust, as furnishing evidence of piety, is truly the Spirit of God or is a spirit of delusion.