Rashi on Numbers 12:14/רש"י על במדבר י״ב:י״ד

1ואביה ירק ירק בפניה IF HER FATHER HAD BUT SPIT IN HER FACE — i.e. if he had shown her an angry face (if he was offended with her), הלא תכלם שבעת ימים SHOULD SHE NOT BE PUT TO SHAME FOR SEVEN DAYS? — It follows therefore à fortiori with respect to the Shechinah (i.e. in the case where God rebukes her in such a stern way) that she ought to be put to shame for fourteen days!) But since there is a rule דין לבא מן הדין להיות כנדון “It is sufficient for a law that is derived by a conclusion a fortiori (הבא מן הדין) to be only as strict as the law from which it is derived (נדון), and not go beyond it, therefore even as a consequence of My reprimand, תסגר שבעת ימים LET HER BE SHUT OUT [FROM THE CAMP] SEVEN DAYS only (Sifrei Bamidbar 106; Bava Kamma 25a).

2ואחר תאסף AND AFTER THAT LET HE BE GATHERED IN AGAIN — I say that all the different forms of the root אסף which are employed in reference to lepers (cf. e. g. 2 Kings 5:6, 11) are used because he (the leper) is sent forth from the camp and when he becomes healed he is taken again into the camp; — on this account it uses of him the term אסיפה, which has the meaning of “taking in” something that was outside.