Kommentar zu Schemot 34:15

ואכלת מזבחו AND THOU EAT OF HIS SACRIFICE — You might perhaps think that there is no punishable offence in eating of it, this is not so, but I will account it unto you as though you consent to his idolatrous worship because through this (through partaking of his meals) you will be induced to take your daughters unto your sons (cf. Avodah Zarah 8a).

AND THOU EAT OF THEIR SACRIFICE. “You might think that there is no punishment for eating thereof, but I will account it to you as if you agreed to its idolatrous worship.” This is Rashi’s language.⁵²⁵In our text of Rashi the text concludes: “Because through this [partaking of his meals] you will come to take of his daughters to your sons” (as mentioned in the following Verse 16). Rashi thus connects Verse 15 with the following verse, as if to say that the danger of partaking of his meals (mentioned in Verse 15) is that it will lead to the taking of his daughters to your sons (mentioned in Verse 16). Ramban will differ with this interpretation, and hold that Verse 15 constitutes an independent prohibition. But I say in accordance with the opinion of our Rabbis that this constitutes an admonition against eating of the sacrifices to idols, which they said⁵²⁶Abodah Zarah 29b. is forbidden by law of the Torah, and we find no verse concerning it except this one. And the following is the meaning of the verse: “Lest thou make a covenant with the inhabitants of the land, and they go astray after their gods, for they will always be sacrificing to them, and lest they call thee and thou eat of their sacrifice, which he will sacrifice to his gods in his going astray after them, and lest thou take of their daughters unto thy sons.” Thus they are all admonitions following the first prohibition, concerning which He said, lest thou make a covenant.⁵²⁷In Verse 15 before us.

פן תכרות ברית, the Torah immediately explains that the reason why entering into contractual relationships with the inhabitants of the land of Canaan is a non starter, is that once you do that the way is open for them to corrupt you by one of two means; either they will woo your sons to marry their daughters or vice versa. It is only the most elementary courtesy then that they invite you to partake in their festive meals (animals offered to their deities) You will not resist such invitations because you do not want to offend the women whom you love. The truth of this was amply demonstrated even with women who did not live in the land of Canaan in Numbers 22,5.