Sforno on Exodus 3:19/ספורנו על שמות ג׳:י״ט

1כי לא יתן אתכם מלך מצרים להלוך. He will not agree to do this from his own free volition at My request.

2ולא ביד חזקה, I will see to it that he will not even allow you to depart as a result of the plagues I shall inflict on Egypt. I will arrange that as soon as a plague has ceased he will change his mind in order to give Me a chance to inflict further plagues on him as chastisement.