10 “For, behold, in iniquities I was conceived”. As though he were saying, They are conquered that have done what thou, David, hast done: for this is not a little evil and little sin, to wit, adultery and man-slaying. What of them that from the day that they were born of their mother's womb, have done no such thing? Even to them do you ascribe some sins, in order that He may conquer all men when He begins to be judged. David has taken upon him the person of mankind, and has heeded the bonds of all men, has considered the offspring of death, has adverted to the origin of iniquity, and he says, “For, behold, in iniquities I was conceived.” Was David born of adultery; being born of Jesse, a righteous man, and his own wife? What is it that he says himself to have been in iniquity conceived, except that iniquity is drawn from Adam? Even the very bond of death, with iniquity itself is engrained? No man is born without bringing punishment, bringing desert of punishment. A Prophet says also in another place, “No one is clean in Your sight, not even an infant, whose life is of one day upon earth.” For we know both by the Baptism of Christ that sins are loosed, and that the Baptism of Christ avails the remission of sins. If infants are every way innocent, why do mothers run with them when sick to the Church? What by that Baptism, what by that remission is put away? An innocent one I see that rather weeps than is angry. What does Baptism wash off? What does that Grace loose? There is loosed the offspring of sin. For if that infant could speak to you, it would say, and if it had the understanding which David had, it would answer you, Why do you heed me, an infant? Thou dost not indeed see my actions: but I in iniquity have been conceived, “And in sins has my mother nourished me in the womb.”
Apart from this bond of mortal concupiscence was Christ born without a male, of a virgin conceiving by the Holy Ghost. He cannot be said to have been conceived in iniquity, it cannot be said, In sins His mother nourished Him in the womb, to whom was said, “The Holy Ghost shall come upon you, and the Virtue of the Highest shall overshadow you.” It is not therefore because it is sin to have to do with wives that men are conceived in iniquity, and in sins nourished in the womb by their mother; but because that which is made is surely made of flesh deserving punishment. For the punishment of the flesh is death, and surely there is in it liability to death itself. Whence the Apostle spoke not of the body as if to die, but as if dead: “The body indeed is dead,” he says, “because of sin, but the Spirit is life because of righteousness.” How then without bond of sin is born that which is conceived and sown of a body dead because of sin? This chaste operation in a married person has not sin, but the origin of sin draws with it condign punishment. For there is no husband that, because he is an husband, is not subject to death, or that is subject to death for any other reason but because of sin. For even the Lord was subject to death, but not on account of sin: He took upon Him our punishment, and so looses our guilt. With reason then, “In Adam all die, but in Christ shall all be made alive.” For, “Through one man,” says the Apostle, “sin has entered into this world, and through sin death, and so has passed unto all men, in that all have sinned.” Definite is the sentence: “In Adam,” he says, “all have sinned.” Alone then could such an infant be innocent, as has not been born of the work of Adam.
11. “For, behold, truth You have loved: uncertain and hidden things of Your wisdom, You have manifested to me”. That is, You have not left unpunished even the sins of those whom Thou dost pardon. “Truth You have loved:” so mercy You have granted first, as that You should also preserve truth. Thou pardonest one confessing, pardonest, but only if he punishes himself: so there are preserved mercy and truth: mercy because man is set free; truth, because sin is punished. “Uncertain and hidden things of Your wisdom You have manifested to me.” What “hidden things”? What “uncertain things”? Because God pardons even such. Nothing is so hidden, nothing so uncertain. For this uncertainty the Ninevites repented, for they said, though after the threatenings of the Prophet, though after that cry, “Three days and Nineve shall be overthrown:” they said to themselves, Mercy must be implored; they said in this sort reasoning among themselves, “Who knows whether God may turn for the better His sentence, and have pity?” It was “uncertain,” when it is said, “Who knows?” on an uncertainty they did repent, certain mercy they earned: they prostrated them in tears, in fastings, in sackcloth and ashes they prostrated them, groaned, wept, God spared. Nineve stood: was Nineve overthrown? One way indeed it seems to men, and another way it seemed to God. But I think that it was fulfilled that the Prophet had foretold. Regard what Nineve was, and see how it was overthrown; overthrown in evil, built in good; just as Saul the persecutor was overthrown, Paul the preacher built. Who would not say that this city, in which we now are, was happily overthrown, if all those madmen, leaving their triflings, were to run together to the Church with contrite heart, and were to call upon God's mercy for their past doings? Should we not say, Where is that Carthage? Because there is not what there was, it is overthrown: but if there is what there was not, it is built. So is said to Jeremiah, “Behold, I will give to you to root up, to dig under, to overthrow, to destroy,” and again, “to build, and to plant.” Thence is that voice of the Lord, “I will smite and I will heal.” He smites the rottenness of the deed, He heals the pain of the wound. Physicians do thus when they cut; they smite and heal; they arm themselves in order to strike, they carry steel, and come to cure. But because great were the sins of the Ninevites, they said, “Who knows?” This uncertainty had God disclosed to His servant David. For when he had said, before the Prophet standing and convicting him, “I have sinned:” straightway he heard from the Prophet, that is, from the Spirit of God which was in the Prophet, “Your sin is put away from you.” “Uncertain and hidden things” of His wisdom He manifested to him.
12. “You shall sprinkle me,” he says, “with hyssop, and I shall be cleansed”. Hyssop we know to be a herb humble but healing: to the rock it is said to adhere with roots. Thence in a mystery the similitude of cleansing the heart has been taken. Do thou also take hold, with the root of your love, on your Rock: be humble in your humble God, in order that you may be exalted in your glorified God. You shall be sprinkled with hyssop, the humility of Christ shall cleanse you. Despise not the herb, attend to the efficacy of the medicine. Something further I will say, which we are wont to hear from physicians, or to experience in sick persons. Hyssop, they say, is proper for purging the lungs. In the lung is wont to be noted pride: for there is inflation, there breathing. It was said of Saul the persecutor as of Saul the proud, that he was going to bind Christians, breathing slaughter: he was breathing out slaughter, breathing out blood, his lung not yet cleansed. Hear also in this place one humbled, because with hyssop purged: “You shall wash me,” that is, shall cleanse me: “and above snow I shall be whitened.” “Although,” he says, “your sins shall have been like scarlet, like snow I will whiten.” Out of such men Christ does present to Himself a vesture without spot and wrinkle. Further, His vesture on the mount, which shone forth like whitened snow, signified the Church cleansed from every spot of sin.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)