1 Behold what manner of love the Father has bestowed on us, that we should be called children of God! Therefore the world does not know us, because it did not know Him.
2 Beloved, now we are children of God; and it has not yet been revealed what we shall be, but we know that when He is revealed, we shall be like Him, for we shall see Him as He is.
3 And everyone who has this hope in Him purifies himself, just as He is pure.
Behold what manner (v.1) — The word “Behold” is in the plural. It is not an exclamation but a command to all believers. The word [translated] “what-manner-of” always indicates astonishment and usually admiration also. — Vine, page 49.
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called (v.1) — The Apostle speaks of the relationship as a calling, rather than saying that we have become children of God; he thus suggests the dignity of the relationship. — Vine, page 49.
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know (v.1, 2x) — Suggests that the world has not even begun to gain by experience a knowledge of the children of God. — Vine, page 50.
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The “now” (v.2) is set in contrast to the future. That we are children suggests that, blessed as the relationship is, this is not the final state. — Vine, page 50.
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“not yet” (v.2) is set in contrast to “now.” … That we are now children of God is a foretaste of what we are going to be. The present state is the guarantee of future glories. — Vine, page 50.
when He is revealed (v.2) — Since John was writing to Jewish kingdom believers, this cannot be referring to the Rapture. However, Paul wrote several times about our future glorification (see quote below).
know (v.2) — This is a different word than that translated “know in v.1. This is “an absolute certainty intuitively realized.”
To be like Christ (v.2) will involve many things including an immortal, glorified body. … Christlikeness or conformity to His moral image is God’s final goal for His children (Romans 8:29-30; 1 Corinthians 15:49; Philippians 3:21). — Grace, page 2221.
Everyone who has this hope (v.3) — all believers.
The hope (v.3) is not described as being in the believer. It is a hope set on Christ, a hope that rests upon Him. — Vine, page 52.
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purifies (v.3) — The purification is from everything that is inconsistent with the character and will of the Lord. This truth is directed against the Gnostic teaching that sin does not pollute the enlightened person. The tense is the continuous present and thus indicates the habit of resisting every defiling influence and keeping oneself free from it. — Vine, page 52.
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