John Lightfoot on Matthew 8:2

[Thou canst make me clean.] The doctrine in the law concerning leprosy paints out very well the doctrine of sin.

I. It teacheth, that no creature is so unclean by a touch as man. Yea, it may with good reason be asked, whether any creature, while it lived, was unclean to the touch, beside man? That is often repeated in the Talmudists, that "he that takes a worm in his hand, all the waters of Jordan cannot wash him from his uncleanness"; that is, while the worm is as yet in his hand; or the worm being cast away, not until the time appointed for such purification be expired. But whether it is to be understood of a living or dead worm, it is doubted, not without cause, since the law, treating of this matter, speaketh only of those things that died of themselves. See Leviticus 11:31: "Whosoever shall touch them when they be dead," &c.: and verse 32, "Upon whatsoever any of them, when they are dead, shall fall," &c. But whether he speaks of a living worm, or a dead, uncleanness followed by the touch of it for that day only: for "he shall be unclean (saith the law) until the evening": but the carcase of a man being touched, a week's uncleanness followed. See Numbers 19.

II. Among all the uncleannesses of men, leprosy was the greatest, inasmuch as other uncleannesses separated the unclean person, or rendered him unclean, for a day, or a week, or a month; but the leprosy, perhaps, for ever.

III. When the leper was purified, the leprosy was not healed: but the poison of the disease being evaporated, and the danger of the contagion gone, the leper was restored to the public congregation. Gehazi, the servant of Elisha, was adjudged to perpetual leprosy; and yet he was cleansed, and conversed with the king (2 Kings 8:5); cleanse, not healed. Thus under justification and sanctification there remain still the seeds and filth of sin.

IV. He that was full of the leprosy was pronounced clean; he that was otherwise, was not. Leviticus 13:12; "If the leprosy shall cover the whole body from head to foot, thou shalt pronounce him clean," &c. A law certainly to be wondered at! Is he not clean, till the whole body be infected and covered with the leprosy? Nor shalt thou, O sinner, be made clean without the like condition. Either acknowledge thyself all over leprous, or thou shalt not be cleansed.