2 Accordingly John confessed Him: as you have heard that when Jesus was making many disciples, and they reported to John as if to excite him to jealousy,— for they told the matter as if moved by envy, “Lo, he is making more disciples than you,”— John confessed what he was, and thereby merited to belong to Him, because he dared not affirm himself to be that which Jesus is. Now this is what John said: “A man cannot receive anything, unless it be given him from heaven.”
Therefore Christ gives, man receives. “You yourselves bear me witness that I said, I am not the Christ, but that I am sent before Him. He that has the bride is the Bridegroom; but the friend of the Bridegroom, who stands and hears Him, rejoices greatly because of the Bridegroom's voice.” Not of himself did he give himself joy. He that will have joy of himself shall be sad; but he that will have his joy of God will ever rejoice, because God is everlasting. Do you desire to have everlasting joy?
Cleave to Him who is everlasting. Such an one John declared himself to be. “Because of the Bridegroom's voice, the friend of the Bridegroom rejoices,” not because of his own voice, and “stands and hears.” Therefore, if he falls, he hears Him not: for of a certain one who fell it is said, “And he stood not in the truth;” this is said of the devil. It behooves the Bridegroom's friend, then, “to stand and to hear.” What is it to stand? It is to abide in His grace, which he received.
And he hears a voice at which he rejoices. Such was John: he knew whereof he rejoiced; he did not arrogate to himself to be what he was not; he knew himself as one enlightened, not the enlightener. “But that was the true Light,” says the evangelist, “that lightens every man coming into this world.” If “every man,” then also John himself; for he too is of men. Moreover, although none has arisen among them that are born of women greater than John, yet he was himself one of those that are born of women.
Is he to be compared with Him who, because He willed it, was born by a singular and extraordinary birth? For both generations of the Lord are unexampled, both the divine and the human: by the divine He has no mother; by the human, no father. Therefore John was but one of the rest: of greater grace, however, so that of those born of women none arose greater than he; so great a testimony he gave to our Lord Jesus Christ as to call Him the Bridegroom, and himself the Bridegroom's friend, not worthy however to loose the latchet of the Bridegroom's shoe.
You have already heard much on this point, beloved: let us look to what follows; for it is somewhat hard to understand. But as John himself says, that “no man can receive anything, unless it be given him from heaven,” whatever we shall not have understood, let us ask Him who gives from heaven: for we are men, and cannot receive anything, except He, who is not man, give it us.
Source: Tractates on the Gospel of John (New Advent)