Commento su Bega'im 5:2

הלך שער לבן – that he had been certified as a leper for its sake [of the white hair].

Introduction In all of the cases in this mishnah, there were signs of impurity in the nega and the person was declared impure. And then those signs disappeared and new signs arose. The question is: does this count as a new nega or does he continue in his earlier state of impurity?

וחזר שער לבן – other in its place.

If one had been certified unclean on account of white hair, and the white hair disappeared and other white hair appeared, And so also in the case of quick flesh or a spreading, Whether this occurred in the beginning, at the end of the first week, at the end of the second week, or after he had been released from uncleanness, he is regarded as being in the same position as before. In the first example, the sign of impurity was the white hairs. After having been declared impure, the original white hairs disappeared and either new white hairs came in their place, or quick flesh or the spreading of the original nega, both of which are also signs of impurity. No matter when this "replacement" occurred, he continues in his earlier state of impurity. In other words, if he was deemed impure immediately, without any weeks of isolation, or if he was deemed impure after a week or two weeks of isolation, or even if he was declared pure after the isolation, if the original signs disappear and new signs, he retains (or regains) his original impurity.

וכן במחיה וכן בפשיון – or that the white hair did not return, but rather that quick flesh resulted which is also a sign of defilement, or that the plague spread.

If he had been certified unclean on account of quick flesh, and the quick flesh disappeared and other quick flesh appeared, And so also in the case of white hair and spreading, Whether this occurred in the beginning, at the end of the first week, at the end of the second week, or after the man had been released from uncleanness, he is regarded as being in the same position as before. This section is the same as section one, except the original sign is quick flesh and not white hairs.

בתחילה בסוף שבוע ראשון – that is to say, whether the declaration of being a certified leper had been at the outset when he was brought to the Kohen, whether at the end of the first week, whether at the end of the second week, whether after the clearance/release, as for example, that it remained unchanged/עמד בעיניו for two weeks and he released him, and after the release, the white hair came and he (i.e., the Kohen) declared him to be a certified leper, in all of these ways if the white hair disappeared and then the white hair returned, or the quick flesh or the spreading. הרי היא כמות שהיתה – that is to say, the defilement remained like it was, for since he has a sign of defilement, even though this is not the same sign that he had at the time of the declaration as a certified leper.

If he had been certified unclean on account of a spreading, and the spreading disappeared and another spreading appeared, And so also in the case of white hair, Whether this occurred at the end of the first week, at the end of the second week, or after the man had been released from uncleanness, he is in the same position as before. Here the original sign is the spreading. "Spreading" cannot be a sign of impurity at the outset, therefore this section does not read "in the beginning."

וחזר הפשיון וכן בשער לבן – but that it (i.e., the Mishnah) doesn’t teach, "וכן המחיה"/and similarly the quick flesh, because when the spreading disappeared and the quick flesh came, sometimes he would be pure, as for example, that the quick flesh diminished the plague from being the size of a split Cilician bean.