Or HaChaim on Leviticus 13:3/אור החיים על ויקרא י״ג:ג׳

1 ומראה הנגע, and the appearance of the affliction, etc. Here we come face to face with the mystical dimension of Psalms 39,7: "man walks about as a mere shadow;" the Psalmist refers to the appearance of raw flesh. When the forces of evil assert themselves in man this makes a visible impression on his flesh. The healthy appearance of his skin disappears. It appears that there is something physically missing, i.e. the skin appears as "deep," as having lost its normal surface. It is remarkable that according to הלכה, one is not ritually impure if this condition covers the entire body, i.e. if this "deepness" leaves no visible mark seeing we cannot detect a contrast with other skin or flesh (compare Shevuot 7).

2וראהו הכהן וטמא אותו, and when the priest takes a look at him he will declare him ritually impure. The Torah made the impurity conditional on the priest declaring him so. This reminds us of a statement in Shabbat 119 that two angels accompany a person on his way home from the synagogue on Friday nights and they examine if this person had made the preparations for the Sabbath prior to going to the synagogue. If he did, one angel commends him (the 'good' angel) exclaiming "may you continue to do so," whereas the second angel [who represents man's negative actions Ed.] says "Amen." The reverse happens when the person in question had not made preparations for the Sabbath before the onset of the Sabbath. At any rate, the Talmud suggests that once a positive or negative momentum has been built it feeds upon itself unless something contrary happens. Seeing that it is the priest's duty to obtain atonement for Israel from their impurities, diseases, etc., G'd has commanded him to concur with the judgment of impurity the afflicted person has been subjected to. This state of impurity will continue until the afflicted person turns into a penitent when G'd will remove the symptoms of impurity from him.