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Bible Hub Commentary 1 John 2:1
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Ellicott's Commentary for English Readers
(4) The third idea that arises from the great fact that God is Light has already been suggested (1John 1:7), but now takes its distinct place in the series. It is the doctrine of Reconciliation and Redemption. St. John does not wish them to contemplate with complacency the probability of sinning; but to remember gratefully, in spite of falls, that the Author and Restorer of Light has provided a remedy both for the offence before God, and for its effect on themselves. First comes the principle that we must not sin; second, the admission that we do sin; third, the consolation for actual sin when it is in spite of sincere zeal for sanctification.
(1) My little children.—Six times in the letter occurs this diminutive of tender and caressing love: 1John 2:12; 1John 2:28; 1John 3:18; 1John 4:4; 1John 5:21. He was aged, he felt a fatherly care for them, he was their spiritual progenitor. (Compare, Galatians 4:9.) The thought of the shame and misery of sin melted his heart. “My child” was what he called out to the lapsed youth, according to Eusebius (H. E. iii. 23).

And not for ours only, but also for the sins of the whole world.—
This statement must not be limited. Its scope is that Christ’s redemption was offered for the whole of mankind, from Adam to the last man. Who lay hold of the redemption, must be determined on other considerations. (Compare, 1John 4:14; John 1:29; John 4:42.) Multitudes may be saved through this redemption who never heard of Christ (Acts 10:34-35; Romans 2:14-15). St. John’s object in introducing this truth here is to rebuke the arrogance of those Christians who looked down on the non-Christian world as outside the Fatherhood and mercies of God. Such an error might be seen, for example, in the heated partisanship of a Crusader or persecutor for a civilisation politically Christian against one outside his own sympathies. (Compare, Titus 3:2-7; Romans 11:17-18.)