I have seen, and have testified that this is the Son of God."

 It is the claim of John that men can enter into that true and real sonship only through Jesus Christ. When he says that it does not come from blood, he is using Jewish thought, for the Jews believed that a physical son was born from the union of the seed of the father with the blood of the mother. This sonship does not come from any human impulse or desire or from any act of the human will; it comes entirely from God. We cannot make ourselves sons of God; we have to enter into a relationship which God offers us. No man can ever enter into friendship with God by his own will and power; there is a great gulf fixed between the human and the divine. Man can only enter into friendship with God when God himself opens the way. 