Verse 4. - The participial substantive ὁ λέγων now takes the place of ἐάν with the subjunctive, but the two are equivalent (cf. 1 John 1:6, which is almost exactly parallel to this, and shows what "knowing him" really is, viz. having fellowship with him, just as not keeping his commandments is the same as walking in darkness). St. John says, μὴ τηρῶν, not, οὐ τηρῶν, the case being hypothetical - if there be such a man, he is a liar, and has no idea of truth (see on 1 John 1:8). He must have lost the very power of recognizing truth to maintain that he knows Christ, when he habitually transgresses his commands. It is no great thing, as Bode says, to know as the devils do, who "believe and tremble."

2:3-11 What knowledge of Christ can that be, which sees not that he is most worthy of our entire obedience? And a disobedient life shows there is neither religion nor honesty in the professor. The love of God is perfected in him that keeps his commandments. God's grace in him attains its true mark, and produces its sovereign effect as far as may be in this world, and this is man's regeneration; though never absolutely perfect here. Yet this observing Christ's commands, has holiness and excellency which, if universal, would make the earth resemble heaven itself. The command to love one another had been in force from the beginning of the world; but it might be called a new command as given to Christians. It was new in them, as their situation was new in respect of its motives, rules, and obligations. And those who walk in hatred and enmity to believers, remain in a dark state. Christian love teaches us to value our brother's soul, and to dread every thing hurtful to his purity and peace. Where spiritual darkness dwells, in mind, the judgment, and the conscience will be darkened, and will mistake the way to heavenly life. These things demand serious self-examination; and earnest prayer, that God would show us what we are, and whither we are going.He that saith I know him,.... God or Christ, as the Gnostics did, who pretended to great, even perfect, knowledge of divine things:

and keepeth not his commandments; which the above persons had no regard to, and as many who profess great light and knowledge in our days show no concern for:

is a liar; he contradicts what he says, and gives the lie to it; for though in words he professes to know God, in works he denies him, and which betrays his ignorance of him:

and the truth is not in him; there is no true knowledge of God and Christ in him; nor is the truth of the Gospel in his heart, however it may be in his head; nor is the truth of grace in him, for each of these lead persons to obedience. The Ethiopic version renders it, "the truth of God is not with him"; See Gill on 1 John 1:8.