Musar על בבא מציעא 116:8

The paragraph commencing with וכי יגור אתכם גר, "When a stranger (convert) resides amongst you, etc" (19,33), contains an allusion to Abraham, the first convert to Judaism. He also became the first אזרח, natural born citizen, as we know from Psalms 89,1, which, according to all our sources, is a reference to Abraham. The reason the Torah alludes to Abraham as the first convert is to teach us not to accuse others of shortcomings when we ourselves suffer from the same type of shortcoming. To denigrate a stranger is to forget that we ourselves started our career as a nation as strangers. In the words of Baba Metzia 59b: "If one's family tree contains the name of someone who has been legally hanged, he should not even say to a fellow "hang this fish up for me," for the very mention of hanging is a reminder of a blemish in his own family." The Israelites were guilty of idol worship while in Egypt as well as of many abominable practices. How then could they dare remind a convert of his pagan past? Abraham himself chose exile (Shemot Rabbah 59) for his descendants in preference to their having to linger in purgatory. Purgatory comprises both the dimension of dryness and wetness. The dryness expresses itself in the fire, the wetness in a form of snow. As an allusion to this, the Torah here continues with the prohibition to sacrifice to the fire-god Moloch (20,2-5) a warning of what is in store for Esau and his followers. The Torah speaks only of people who sacrifice some of their offspring to Moloch. The author of Semag writes an explanation as a reply to the heretics; however, the true reason for this is analogous to the statement of our sages on Genesis 21,12 where Abraham did not want to expel Hagar and Ishmael. G–d told him there that his principal heirs would be "part of Isaac." Just as the Torah referred in that case to "part of Isaac," so here too the syntax of the Torah speaks of the likely event, i.e. that someone offers some of his offspring as a sacrifice to that deity. Just as only part of Isaac's descendants turned away from the Abrahamitic tradition, i.e. Esau, so the Torah, by speaking of "some offspring being offered to the Moloch," reassures us that it is inconceivable that a descendant of Isaac would sacrifice all of his offspring to such a deity. The Torah continues in 20,7: והתקדשתם. This is a reference to Jacob. He had succeeded in attaining sanctity of his body.