1 And the LORD said to Moses, "Yet I will bring one more plague upon Pharaoh and upon Egypt. Afterward he will let you go from here. When he lets you go, he shall surely thrust you out from here altogether. 2 Speak now in the ears of the people, and let every man borrow of his neighbor and every woman of her neighbor, jewels of silver and jewels of gold." 3 And the LORD gave the people favor in the sight of the Egyptians. Moreover, the man Moses was very great in the land of Egypt, in the sight of Pharaoh's servants, and in the sight of the people.
4 And Moses said, "Thus says the LORD: 'About midnight I will go out into the midst of Egypt. 5 And all the first-born in the land of Egypt shall die, from the first-born of Pharaoh who sits upon his throne, even to the first-born of the maid-servant who is behind the mill, and all the first-born of beasts. 6 And there shall be a great cry throughout all the land of Egypt, such as there has been none like it, nor shall be like it anymore. 7 But against any of the children of Israel a dog shall not move his tongue, against man or beast, so that you may know how the LORD puts a difference between the Egyptians and Israel.' 8 And all these servants of yours shall come down to me and bow down themselves to me, saying, 'Depart—you and all the people who follow you.' And after that I will depart." And he went out from Pharaoh in a great anger.
9 And the LORD said to Moses, "Pharaoh will not listen to you so that my wonders may be multiplied in the land of Egypt." 10 And Moses and Aaron did all these wonders before Pharaoh, and the LORD hardened Pharaoh's heart so that he would not let the children of Israel depart from his land.
[v.2] - This message would have been conveyed to the people of Israel after Moses and Aaron left the presence of Pharaoh.
[v.4-8] - In these verses, Moses outlines to Pharaoh what will be the final judgment upon him and the Egyptians. God had shown Himself able to put the Egyptian gods to shame. With all of their gods defeated, it was time for the Egyptians to know the power of God. This judgment is the killing of all the first-born of Egypt, whether of man or of any of the animals (see Exodus 12:29). Furthermore, there will be a great cry throughout the land because of the magnitude of this judgment upon the Egyptians (see Exodus 12:30). None of the Israelites were affected by this, as with the previous judgments. This is to show that there is a separation between Egypt and Israel, or to put it in a different way, Israel is distinguished from Egypt as God's chosen people (Deuteronomy 7:6, 14:2, 26:18-19; 1st Peter 2:9). Moses then told Pharaoh that his servants will come to him, bow to him, and bid him depart from Egypt (Exodus 12:33). Pharaoh was given a warning of this judgment back in Exodus 4:23. God's vengeance upon Pharaoh and the Egyptians would be the taking of each and every first-born of the Egyptians, as the Egyptians had taken God's first-born. God could have done this first, which was the worst of all the previous judgments, but He chose to use it as a last option to show that He is slow to bring His wrath (Nahum 1:3; Psalm 103:8, 145:8; Joel 2:13; Jonah 4:2). Vessels fitted for destruction will have their purpose fulfilled, yet God will do this enduring with much patience so that he might make known the riches of his glory for the vessels of mercy (Romans 9:22-23). This is essentially the mechanics behind the message of the Gospel. God's wrath is impending to those who do not repent of their sins and turn to Christ, trusting in Him wholly. Those who do not give heed to the warning, will take upon themselves the wrath of God. Those who do give heed to the warning, will be adopted as children of God and receive the inheritance of eternal life in the kingdom of Heaven. The Apostle Paul put it best when he said, "In [Christ] you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also after you believed, you were sealed with that holy Spirit of promise, which is the earnest of our inheritance until the redemption of the purchased possession, to the praise of his glory" (Ephesians 1:13-14).