11 Brethen, return in thought to your own homes. I speak of carnal, I speak of earthly things; I speak after the manner of men, for the infirmity of your flesh. Many of you have, many of you wish to have, many, though you wish not to have, still have had wives; many who do not at all wish to have wives, are born of the wives of your fathers. This is a feeling that touches every heart. There is no man so alien from mankind in human affairs as not to feel what I say. Suppose that a man, having set out on a journey, had commended his bride to the care of his friend: “See, I pray you, you are my dear friend; see to it, lest in my absence some other may perchance be loved in my stead.”
Then what sort of a person must he be, who, while the guardian of the bride or wife of his friend, does indeed endeavor that none other be loved, but if he wishes himself to be loved instead of his friend, and desires to enjoy her who was committed to his care, how detestable must he appear to all mankind! Let him see her gazing out of the window, or joking with some one somewhat too heedlessly, he forbids her as one who is jealous. I see him jealous, but let me see for whom he is jealous; whether for his absent friend or for his present self.
Think that our Lord Jesus Christ has done this. He has committed His bride to the care of His friend; He has set out on a journey to a far country to receive a kingdom, as He says Himself in the Gospel, but yet is present in His majesty. Let the friend who has gone beyond the sea be deceived; and if he is deceived, woe to him who deceives! Why do men attempt to deceive God—God who looks at the hearts of all, and searches the secrets of all? But some heretic shows himself, and says, “'Tis I that give, 'tis I that sanctify, 'tis I that justify; go not to that other sect.”
He does well indeed to be jealous, but see for whom. “Go not to idols,” says he—he is rightly jealous; “nor to diviners,”— still rightly jealous. Let us see for whom he is jealous: “What I give is holy, because it is I that give it; he is baptized whom I baptize; he whom I baptize not is not baptized.” Hear the friend of the bridegroom, learn to be jealous for your friend; hear His voice who is “He that baptizes.” Why desire to arrogate to yourself what is not yours? Is he so very absent who has left here his bride?
Do you not know, that He who rose from the dead is sitting at the right hand of the Father? If the Jews despised Him hanging on the tree, do you despise Him sitting in heaven? Be assured, beloved, that I suffer great grief of this matter; but, as I have said, I leave the rest to your thoughts. I cannot utter it if I speak the whole day. If I bewail it the whole day, I do not enough. I cannot utter it, if I should have, as the prophet says, “a fountain of tears;” and were I changed into tears, and to become all tears, were I turned into tongues, and to become all tongues, it were not enough.
Source: Tractates on the Gospel of John (New Advent)