Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not.
Behold - calling attention to something wonderful, little as the world sees to admire. This verse is connected with 1 John 2:29. All our doing of righteousness is a mere sign that God, of His matchless love, has adopted us as children: it does not save us, but indicates that we are saved of His grace.
What manner of - how surpassingly gracious on His part, how precious to us!
Love ... bestowed. He does not say that God hath given us some gift, but love itself, the fountain of all blessings; not for our works, but of His grace (Luther).
That, х hina (G2443)] - resulting in. The effect aimed at in the bestowal of His love is, 'that we should be called children of God.'
Should be called - should have such a glorious title (imaginary as it seems to the world), along with the glorious reality. With God to call is to make really. Who so great as God? What nearer relationship than that of sons? 'Aleph (') A B C, Vulgate, add, 'And we ARE so' really.
Therefore - because 'we are (really) so.
Us - the children, like the Father.
It knew him not - namely, the Father. 'If they who regard not God hold thee in any account, feel alarmed about thy state' (Bengel). Contrast 1 John 5:1. The world's whole course is one great act of non-recognition of God.