Verse 5. But whoso keepeth his word. That is, what he has spoken or commanded, The term word here will include all that he has made known to us as his will in regard to our conduct.

In him verily is the love of God perfected. He professes to have the love of God in his heart, and that love receives its completion or filling up by obedience to the will of God. That obedience is the proper carrying out, or the exponent of the love which exists in the heart. Love to the Saviour would be defective without that, for it is never complete without obedience. If this be the true interpretation, then the passage does not make any affirmation about sinless perfection, but it only affirms that if true love exists in the heart, it will be carried out in the life; or that love and obedience are parts of the same thing; that one will be manifested by the other; and that where obedience exists, it is the completion or perfecting of love. Besides, the apostle does not say that either the love or the obedience would be in themselves absolutely perfect; but he says that one cannot fully develope itself without the other.

Hereby know we that we are in him. That is, by having in fact such love as shall insure obedience. To be in him, is to be united to him; to be his friends. See Barnes "Joh 6:56"; See Barnes "Ro 13:14".