Behold! It means to observe, to see with attention. Yet, I have read this verse many times, but never really stopped to think about it. I've never taken the time to observe it and to see it with attention.
What manner of love the Father has bestowed upon us, that we should be called the sons of God!
He was in the world, and the world was made by him, and the world knew him not. He came unto his own, and his own received him not. But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world. (John 1:10-14, 29 KJV)
As sinners we deserve the just penalty for missing the mark of God's righteous standard and for thinking we can stand on our own self righteousness. Yet, He came in the flesh to a sinful world of people and was rejected by the majority and crucified, taking the just penalty for our sin on Himself so that as many as recieved Him and believed on His name would be given the power to become sons of God. He has to give the power to us to become the sons of God because we can not do it on our own power. It doesn't happen by heritage, or by our own will. It happens by the will and power of God. He makes us willing to receive Him and know Him. It is all of His own doing that He bestows His love on us and makes us know and desire to accept Him. What manner of love the Father has bestowed upon us!