פּירוש אויף שמות 3:19

לא יתן אתכם מלך מצרים להלך THE KING OF EGYPT WILL NOT LET YOU GO, if I do not (ולא) show him My strong hand (יד חזקה) — it is as much as to say: so long as I do not let him feel My strong hand he will not let you go.

ואני ידעתי כי לא יתן אתכם מלך מצרים להלוך, “I know already that the King of Egypt will not permit you to go;” G-d revealed to Moses beforehand that Pharaoh would become obstinate; He told Moses this in advance so that he would not become discouraged over Pharaoh’s refusal. Seeing that in the event Moses still did become discouraged, we can imagine how much more discouraged he would have been if G-d had not foretold him that.

V’LO B’YAD CHAZAKAH’ (AND NOT BY A MIGHTY HAND). “So long as I do not let him feel My mighty hand he will not let you go.” Thus the words of Rashi.²⁴³The sense of the verse according to Rashi is thus: “except by a mighty hand.” It is so translated in the J.P.S. translation. Ramban will suggest its meaning to be: “and not even by a mighty hand.”
The correct interpretation in my opinion is: “The king of Egypt will not give you leave to go by plea, and not [even] by a mighty hand, until I will put forth My hand with all My wonders which I will do in his midst,²⁴⁴Verse 20. by a mighty hand, and by an outstretched arm, and by great terrors, and by signs and by wonders.²⁴⁵Deuteronomy 4:35. In the verse there, the phrase “by trials and by wonders” is listed first. And after that he will let you go.”²⁴⁴Verse 20. Indeed, all these manifestations came upon him before he gave them leave to go.