Exodus 7:4

“But Pharaoh shall not hearken unto you, etc.] Regard not what they said, nor answer the demand they made, or obey the command of God delivered by them to him: this the Lord apprised them of, that they might not be discouraged, and conclude their labour would be in vain, their attempts fruitless, and they should never gain their point, but spend their time, and expose themselves to danger to no purpose: that I may lay mine hand upon Egypt; the inhabitants of Egypt, smiting them with one plague after another, and particularly with the last, slaying their firstborn; every plague was a stroke of his hand, and an effect of his mighty power and vengeance, and more especially that: and bring forth…”

“I may lay mine hand upon Egypt, &c.--The succession of terrible judgments with which the country was about to be scourged would fully demonstrate the supremacy of Israel's God.”

“that I: Exo 9:3, Exo 10:1, Exo 11:9; Jdg 2:15; Lam 3:3 armies: Exo 6:26, Exo 12:51 by great: Exo 6:6; Pro 19:29; Isa 26:9; Eze 14:21, Eze 25:11, Eze 30:14, Eze 30:19; Rev 15:4, Rev 16:7; Rev 19:2 Exodus 7:5”

“את־ידי ונתתּי: "I will lay My hand on Egypt," i.e., smite Egypt, "and bring out My armies, My people, the children of Israel." צבאות (armies) is used of Israel, with reference to its leaving Egypt equipped ( Exo 13:18) and organized as an army according to the tribes (cf. Exo 6:26 and Exo 12:51 with Num 1 and 2), to contend for the cause of the Lord, and fight the battles of Jehovah. In this respect the Israelites were called the hosts of Jehovah. The calling of Moses and Aaron was now concluded. Exo 7:6 and Exo 7:7 pave the way for the account of their performance of the duties consequent upon their call. Exodus 7:8”