Commentaire sur L’Exode 12:48

ועשה פסח AND HE WILL KEEP THE PASSOVER (the words may mean, then he shall keep the Passover) — One might think that this verse implies that any-one who becomes a proselyte (גר) must keep the Passover-offering rite immediately after his circumcision (even though this has not taken place just before Passover), therefore Scripture states והיה כאזרח הארץ “but he shall be as a native of the land”. How is it in the case of a native? He brings the offering on the fourteenth! So, too, a proselyte must bring it only on the fourteenth (Mekhilta d'Rabbi Yishmael 12:49).

וכי יגור אתך גר, "When a stranger will sojourn with you, etc." This was Moses' authority to accept converts from amongst the Egyptians. The reason the Torah writes אתך, "with you" (sing), is that such conversions had to be personally approved by Moses. There is also a hint here that G'd agreed to this only reluctantly, i.e. לרצון משה, and that is why the Torah wrote אתך גר, "he is a stranger (proselyte) with you, (but not with Me). G'd's reluctance was due to Moses' inability to examine G'd's hidden reasons. We all know what the result of Moses' accepting such proselytes was and how they triggered the sin of the golden calf.

וכל ערל, A Jew whose brother had died from the after-effects of the circumcision and has therefore not been circumcised himself must not eat from this offering. (Compare Rashi)