Thomas Aquinas, on Ps 50:7

“For behold I was conceived in iniquities; and in sins did my mother conceive me.”

“"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.”

Imported from an open dataset — not yet checked against the printed edition.