Now the Lord had said to Moses, “I will bring one more plague on Pharaoh and on Egypt. After that, he will let you go from here, and when he does, he will drive you out completely. 2 Tell the people that men and women alike are to ask their neighbors for articles of silver and gold.” 3I'll just note again that we don't know how God is doing all this talking. Does Moses hear the voice in his head, does it come down from the sky, is there yet another burning bush? Anyway, KJV has it that the people are to "borrow" the silver and gold from their (presumably Egyptian) neighbors, which is obviously stealing since their intention is to make off with it. Again, isn't there going to be a commandment about that? Hmm.
3 (The Lord made the Egyptians favorably disposed toward the people, and Moses himself was highly regarded in Egypt by Pharaoh’s officials and by the people.)The parentheses are added by the translators, of course. I'm not sure why. Anyway apparently this is supposed to explain why the Egyptians handed over their valuables to slaves. In any case it's quite odd.
The cattle are already all dead, remember? They were exterminated in the fifth plague, and then, even though they were already all dead, they were killed again in the hail. I need hardly point out that there seems to be something a little bit wrong about murdering all these people, maybe? None of them is responsible for Pharaoh refusing to let the Israelites go. God is responsible for that, as he keeps hardening Pharaoh's heart.
4 So Moses said, “This is what the Lord says: ‘About midnight I will go throughout Egypt. 5 Every firstborn son in Egypt will die, from the firstborn son of Pharaoh, who sits on the throne, to the firstborn son of the female slave, who is at her hand mill, and all the firstborn of the cattle as well. 6
There will be loud wailing throughout Egypt—worse than there has ever been or ever will be again. 7 But among the Israelites not a dog will bark at any person or animal.’ Then you will know that the Lord makes a distinction between Egypt and Israel. 8Aha, now we get it. This is not the universal God most Christians and Jews understand today. This God is specific to the Hebrews and cares only about them. The whole point of this exercise is to prove that.
All these officials of yours will come to me, bowing down before me and saying, ‘Go, you and all the people who follow you!’ After that I will leave.” Then Moses, hot with anger, left Pharaoh.
9 The Lord had said to Moses, “Pharaoh will refuse to listen to you—so that my wonders may be multiplied in Egypt.” 10 Moses and Aaron performed all these wonders before Pharaoh, but the Lord hardened Pharaoh’s heart, and he would not let the Israelites go out of his country.
So there you go. God is causing Pharaoh not to let the people go for the purpose of giving himself an excuse to murder all the firstborn sons of Egypt. He is not murdering the firstborn sons for the purpose of freeing the Israelites, he is doing it to prove that he doesn't give a shit about Egyptians, and is capable of murdering them. That is the entire point of this story.