A.T. Robertson Commentary 1 John 2

My little children (τεκνια μου). Tender tone with this diminutive of τεκνον (child), again in 2:12; 3:18, but παιδια in 2:14. John is now an old man and regards his readers as his little children. That attitude is illustrated in the story of his visit to the robber to win him to Christ.

That ye may not sin (ινα μη αμαρτητε). Purpose (negative) clause with ινα μη and the second aorist (ingressive, commit sin) active subjunctive of αμαρτανω, to sin. John has no patience with professional perfectionists (1:8-10), but he has still less with loose-livers like some of the Gnostics who went to all sorts of excesses without shame.

If any man sin (εαν τις αμαρτη). Third-class condition with εαν and second aorist (ingressive) active subjunctive again, "if one commit sin."

We have (εχομεν). Present active indicative of εχω in the apodosis, a present reality like εχομεν in 2 Corinthians 5:1.

An advocate (παρακλητον). See on Joh 14:16,26; 15:26; 16:7 for this word, nowhere else in the N.T. The Holy Spirit is God's Advocate on earth with men, while Christ is man's Advocate with the Father (the idea, but not the word, in Ro 8:31-39; Hebrews 7:25). As δικαιος (righteous) Jesus is qualified to plead our case and to enter the Father's presence (Hebrews 2:18).

And he (κα αυτος). He himself in his own person, both priest and sacrifice (Hebrews 9:14).

The propitiation (ιλασμος). Late substantive from ιλασκομα (Luke 18:13; Hebrews 2:17), in LXX, Philo, Plutarch, in N.T. only here and 4:10. Christ himself is the means of propitiation for (περ concerning) our sins. See ιλαστηριον in Ro 3:15.

For the whole world (περ ολου του κοσμου). It is possible to supply the ellipsis here of των αμαρτιων (the sins of) as we have it in Heb 7:27, but a simpler way is just to regard "the whole world" as a mass of sin (5:19). At any rate, the propitiation by Christ provides for salvation for all (Hebrews 2:9) if they will only be reconciled with God (2 Corinthians 5:19–21).

Hereby (εν τουτω). See this phrase also in 2:5; 3:16,19,24; 4:2,13; 5:2. That is explained by the εαν clause, "if we keep his commandments " (εαν τηρωμεν, condition of the third class, εαν with present active subjunctive, "if we keep on keeping"), the clause itself in apposition with τουτω (locative case).

Know we that we know him (γινοσκομεν οτ εγνωκαμεν αυτον). "Know we that we have come to know and still know him," εγνωκαμεν the perfect active indicative of γινωσκω. The Gnostics boasted of their superior knowledge of Christ, and John here challenges their boast by an appeal to experimental knowledge of Christ which is shown by keeping his (αυτου, Christ's) commandments, thoroughly Johannine phrase (12 times in the Gospel, 6 in this Epistle, 6 in the Apocalypse).

I know him (Εγνωκα αυτον). Perfect active indicative with recitative οτ like quotation marks just before it. This is one of the pious platitudes, cheap claptrap of the Gnostics, who would bob up in meetings with such explosions. John punctures such bubbles with the sharp addition "and keepeth not" (ο μη τηρων, present active linear participle). "The one who keeps on saying: 'I have come to know him,' and keeps on not keeping his commandments is a liar" (ψευστης, just like Satan, John 8:44 and like 1 John 1:8,10), followed by the negative statement as in 1:8,10. There is a whip-cracker effect in John's words.

But whoso keepeth (ος δ' αν τηρη). Indefinite relative clause with modal αν and the present active subjunctive, "whoever keeps on keeping."

Verily (αληθως). Truly, of a truth. This prize is open to all, not confined to a few initiated Gnostic intellectuals or pneumatics.

Hath the love of God been perfected (η αγαπη του θεου τετελειωτα). Perfect passive indicative of τελειοω, stands completed. Probably objective genitive, our love for God, which is realized in absolute obedience (Brooke).

Hereby (εν τουτω). That is by continuous keeping of Christ's commandments, not by loud talk and loose living.