Since Pharaoh continued to refuse to let the Israelites go, for three days, the God engulfed Egypt in darkness. The only light in the land was found with the Israelites themselves—a sign, because from Israel would come Jesus Christ, the light of the world.
"And the Lord said to Moses: Stretch out thy hand towards heaven: and may there be darkness upon the land of Egypt, so thick that it may be felt. And Moses stretched forth his hand towards heaven: and there came horrible darkness in all the land of Egypt for three days. No man saw his brother, nor moved himself out of the place where he was: but wheresoever the children of Israel dwelt there was light.
"And Pharao called Moses and Aaron, and said to them: Go sacrifice to the Lord: let your sheep only, and herds remain; let your children go with you. Moses said: Thou shalt give us also sacrifices and burnt offerings, to the Lord our God. All the flocks shall go with us: there shall not a hoof remain of them: for they are necessary for the service of the Lord our God: especially as we know not what must be offered, till we come to the very place.
"And the Lord hardened Pharao's heart, and he would not let them go. And Pharao said to Moses: Get thee from me, and beware thou see not my face any more: in what day soever thou shalt come in my sight, thou shalt die. Moses answered: So shall it be as thou hast spoken, I will not see thy face any more.
"And the Lord said to Moses: Yet one plague more will I bring upon Pharao and Egypt, and after that he shall let you go and thrust you out. Therefore thou shalt tell all the people that every man ask of his friend, and every woman of her neighbour, vessels of silver, and of gold. And the Lord will give favour to his people in the sight of the Egyptians. And Moses was a very great man in the land of Egypt, in the sight of Pharao's servants, and of all the people.
"And he said: Thus said the Lord: At midnight I will enter into Egypt. And every firstborn in the land of the Egyptians shall die, from the firstborn of Pharao who sitteth on his throne, even to the first born of the handmaid that is at the mill, and all the firstborn of beasts. And there shall be a great cry in all the land of Egypt, such as neither hath been before, nor shall be hereafter. But with all the children of Israel there shall not a dog make the least noise, from man even to beast: that you may know how wonderful a difference the Lord maketh between the Egyptians and Israel. And all these thy servants shall come down to me, and shall worship me, saying: Go forth thou, and all the people that is under thee: after that we will go out. And he went out from Pharao exceeding angry.
But the Lord said to Moses: Pharao will not hear you, that many signs may be done in the land of Egypt. And Moses and Aaron did all the wonders that are written, before Pharao. And the Lord hardened Pharao's heart, neither did he let the children of Israel go out of his land."
- Source: Douay-Rheims 1899 American Edition of the Bible (in the public domain)