Moshe Rabeinu is reluctant to accept his mission to act as the Jewish people’s redeemer, and he questions whether the people will believe him or listen to him – ‘hen lo ya’aminu li v’lo yishm’u l’koli’ (4:1). Hashem responds by reassuring Moshe and providing him with signs to demonstrate that he is a true prophet. G-d guarantees, ‘v’shamu l’kolecha’ (3:18), the people will listen, and they will accept the signs as evidence. The Koznitzer Maggid asks how can G-d possibly guarantee such an outcome to Moshe – by telling Moshe in advance that the people will believe and listen to him, doesn’t that remove their free choice not to listen?
(For a similar question on this week’s parsha, see the posting from last year on the Chasam Sofer’s “kushya atzuma”. One other note: this is different than the general question of G-d's foreknowledge vs. free choice because in this case the choice is revealed in advance to a human audience, which makes the problem a bit more complex.)