Charles Ellicott Commentary Exodus 3:19

"And I know that the king of Egypt will not give you leave to go, no, not by a mighty hand." — Exodus 3:19 (ASV)

I am sure. —Hebrew: I know, which is more suitable, since it is God who speaks, and to him the future is known with as absolute a certainty as the past.

No, not by a mighty hand. —Rather, not even under a mighty hand (ne quidem valida manu castigatus, Rosenmüller). Pharaoh, even when chastised by My mighty hand, will not voluntarily permit your departure .