C. F. Keil and Franz Delitzsch on Exodus 11:1

Exo 11:1

Proclamation of the Tenth Plague; or the Decisive Blow. - Exo 11:1-3. The announcement made by Jehovah to Moses, which is recorded here, occurred before the last interview between Moses and Pharaoh (Exo 10:24-29); but it is introduced by the historian in this place, as serving to explain the confidence with which Moses answered Pharaoh (Exo 10:29). This is evident from Exo 11:4-8, where Moses is said to have foretold to the king, before leaving his presence, the last plague and all its consequences. ויּאמר therefore, in Exo 11:1, is to be taken in a pluperfect sense: “had said;” and may be grammatically accounted for from the old Semitic style of historical writing referred to in the commentary on Gen 2:18-22, as Gen 2:1 and Gen 2:2 contain the foundation for the announcement in Gen 2:4-8. So far as the facts are concerned, Gen 2:1-3 point back to Exo 3:19-22. One stroke more (נגע) would Jehovah bring upon Pharaoh and Egypt, and then the king would let the Israelites go, or rather drive them out. כּלה כּשׁלּחו, “when he lets you go altogether (כּלה adverbial as in Gen 18:21), he will even drive you away.”