Kommentar zu Schemot 9:35

ויחזק לב פרעה, not without an assist from external forces. What happened was precisely as G’d had told Moses and Aaron at the time when G’d appointed Aaron as Moses’ helper; “and I know that the King of Egypt will not voluntarily allow you to leave Egypt.” G’d had even added: “ולא ביד חזקה, I do not want him to give his consent as a sign of his impotence against My strong hand.” G’d wanted Pharaoh to become a penitent while believing he could still offer resistance if he chose. Pharaoh had convinced himself after every plague that G’d had already exhausted the punitive means at His disposal, and that He could do no more to him. [When Maimonides in the third chapter of hilchot Teshuvah enumerates 24 categories of sins which result in the sinners either being unable to do teshuvah, or to face almost insurmountable obstacles in doing so, one of them is this belief that if G’d instead of liquidating them had stopped short of that, this is proof that He could not do any more than He had already done. Pharaoh made this fatal mistake out of his arrogance. Ed.]

'כאשר דבר ה, “as the Lord had said.” G-d had said in Exodus 3,19: “I know that the King of Egypt will not permit you to leave.”

ביד משה, by means of his prophecy that he had been instructed to proclaim. This is the meaning of the expression ביד משה, wherever it occurs