John Gill Commentary 1 John 2:29

"If ye know that he is righteous, ye know that every one also that doeth righteousness is begotten of him." — 1 John 2:29 (ASV)

If you know that he is righteous
That is, Christ, who is righteous as God in his nature and in his works; and as man in his obedience, life, and conversation; and as Mediator, in faithfully discharging the work he undertook; and is the author of an everlasting righteousness, which is imputed by God, revealed in the Gospel, and received by faith; all which they knew, for this is not said as doubting, but rather as taking it for granted that they did know it; "if", or "seeing you know" then it follows;

you know ,
or "know you"; you may assure yourselves,

that everyone that does righteousness ;
not merely works of righteousness, especially in order to justify him before God; for such an one is so far from being born of God, or born again, that he is manifestly in a state of nature, and of opposition to, and enmity against God; he is not subject to him, he does not submit to the righteousness of God, but goes about to establish his own and betrays his ignorance and want grace; but it intends such an one who with the heart believes unto righteousness, and lays hold by faith, and lives upon the righteousness of Christ for justification; and who performs good works in faith, and from a principle of love, not to obtain a justifying righteousness, but because he is justified by the righteousness of Christ: and such an one

is born of him ;
either of God, or rather, of Christ; being regenerated by his Spirit, having his grace implanted in him, as appears by his faith in his righteousness and by his works of righteousness, as fruits of faith; and having his image stamped on him, and he himself formed in him, and so made like unto him; by all which it is evident he is one of his spiritual seed and offspring. The Syriac version reads, "is of him"; belongs to him, is one of his; and this makes way for what is said of adoption in the following chapter and which should begin here.