Ps 50:7

“After this white robes were given to you as a sign that you were putting off the covering of sins and putting on the chaste veil of innocence, of which the prophet said, "Purge me with hyssop, and I shall be cleansed; wash me, and I shall be made whiter than snow." For one who is baptized is seen to be purified according to the law and according to the gospel: according to the law, because Moses sprinkled the blood of the lamb with a bunch of hyssop; according to the gospel, because Christ's garments were white as snow, when in the Gospel he showed forth the glory of his resurrection. One, then, whose guilt is forgiven is made whiter than snow. Thus God said through Isaiah: "Though your sins are as scarlet, I will make them white as snow."”

“"You shall sprinkle me," he says, "with hyssop, and I shall be cleansed" [Psalm 51:7]. 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: [Acts 9:1] 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." [Isaiah 1:18] Out of such men Christ does present to Himself a vesture without spot and wrinkle. [Ephesians 5:27] Further, His vesture on the mount, which shone forth like whitened snow, [Matthew 17:2] signified the Church cleansed from every spot of sin.”

“Behold, with iniquity I was formed Now how could I not sin when the main part of my creation was through coitus, the source of many iniquities? Another explanation: The main part of my creation is from a male and a female, both of whom are full of iniquity. There are many midrashim to this verse, but they do not fit the context of the psalm. conceived me Heb. יחמתני, an expression of heat, as (Gen. 30:38): “And they came into heat (ויחמנה) when they came to drink.””

“"You shall sprinkle me with hyssop." Above, the Psalmist commemorated the benefit of God granted to him as to the grace of prophecy, from which he was raised to hope; here he shows what he hoped for from God. And there were two things. First, he hopes for the removal of the evils he had incurred through sin. Second, he hopes for the restoration of the goods he had lost, at "to my hearing." It should be known that through sin a person first incurs uncleanness. Jer. 2: "You are stained in your iniquity." Second, he incurs disfigurement; hence Lam. 4: "Their face has been made blacker than coals." And he hopes that both of these will be removed from him: namely, spiritual uncleanness and disfigurement. Uncleanness occurs because the affection of a person clings to temporal things and becomes like them; hence if it is joined to baser things, like gold to lead, it becomes base. Hos. 9: "They became abominable like the things they loved." But disfigurement occurs because, by clinging to earthly things, the light of reason in him is obscured, because he is compared to brute animals. Ps. 48: "Man, when he was in honor," etc. And therefore the soul becomes black or obscure. And therefore, as to the first, he says, "You shall sprinkle me with hyssop," where he alludes to the rite of the Old Testament, Num. 19, where on the third day the unclean person was sprinkled with the water of purification, and on the seventh day he was washed with water, and his garments were also washed. The water of purification was made with hyssop. And therefore he says, "You shall sprinkle me with hyssop." And that water was made from the ash of a red heifer, through which Christ was prefigured. Hence by that sprinkling which he asks for, the sprinkling of the blood of Christ is signified. 1 Pet. 1: "In the sprinkling of the blood of Christ." Heb. 12: "You have come to the mountain... and to the sprinkling of blood that speaks better than Abel." This was done with hyssop. Hyssop is a plant that clings to the earth and cures swelling, as the Gloss says; and it corresponds to faith, which has humility, because through faith the intellect is subjected to God. 2 Cor. 10: "Bringing every understanding into captivity to the obedience of Christ." Also, it is rooted in the rock, that is, Christ. Mt. 16: "Upon this rock," etc. "And the rock was Christ," 1 Cor. 10. Also, it dispels the inflation of the human spirit, which is in those who do not obey the faith of Christ. 1 Tim. 6: "If anyone teaches differently and does not acquiesce in the sound words of our Lord Jesus Christ, he is not of his" (Rom. 8). He says therefore: Lord, I have firm hope that you will sprinkle me with the water of purification. Ezek. 36: "I will pour upon you water," etc. "You shall wash me": for after faith, Baptism is necessary. Zech. 13: "There shall be a fountain open to the house of Jacob," etc. Is. 1: "Wash yourselves, be clean." The effect of this washing: "I shall be made whiter than snow," because the blackness will be removed; and this, because the soul will be whiter than snow. Is. 1: "If your sins be as scarlet, they shall be made white as snow." And he says "whiter than snow," because the whiteness of the sanctified soul exceeds all bodily beauty, as is clear in Mt. 17, in the Transfiguration of Christ, whose garments were made white as snow. All the just pertain to the garments of Christ. Is. 49: "You shall be clothed with all of these as with a garment." And through this he designates himself as pertaining to the garment of Christ through Baptism: "As many as have been baptized have put on Christ," says the apostle in Gal. 3.”