EXODUS: The Lord God Sends the Fourth Plague in Egypt; "Thus says the Lord: 'Let My people go, that they may serve Me. Or else, if you will not let My people go, behold, I will send swarms of flies on you and your servants, on your people and into your houses.'"

He sent Moses His servant, and Aaron whom He had chosen. They performed His signs among them, and wonders in the land of Ham. (Psalm 105:26-27)

He spoke, and there came swarms of flies ... in all their territory. (Psalm 105:31) 

And the Lord said to Moses, “Rise early in the morning and stand before Pharaoh as he comes out to the water. Then say to him, ‘Thus says the Lord: “Let My people go, that they may serve Me. Or else, if you will not let My people go, behold, I will send swarms of flies on you and your servants, on your people and into your houses. The houses of the Egyptians shall be full of swarms of flies, and also the ground on which they stand. (Exodus 8:20-21) 

First, the Lord God attacked their "lifeblood", the water in the rivers; then He attacked them with a symbol of many of their gods, frogs; then He attacked their bodies with lice; now, He would attack their land with flies.  Flies were one of many insect nuisances in ancient Egypt. (read "Vermin and Pests in Ancient Egypt") But they were also considered a sacred insect; "these tiny creatures were powerful symbols of resurrection and eternal life.". (read "Sacred Insects in Ancient Egypt") Therefore, the Lord God was going to annoy them with one of their sacred images.

The Lord God continued explaining to Moses, "And in that day I will set apart the land of Goshen, in which My people dwell, that no swarms of flies shall be there, in order that you may know that I am the Lord in the midst of the land. I will make a difference between My people and your people. Tomorrow this sign shall be.”’” And the Lord did so. Thick swarms of flies came into the house of Pharaoh, into his servants’ houses, and into all the land of Egypt. The land was corrupted because of the swarms of flies. (Exodus 8:22-24) 

Isn't that true today also, that there should be an obvious difference between the Lord's people and other people? In the midst of the "plagues" of life, Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust. (II Peter 1:3-4)

Then Pharaoh called for Moses and Aaron, and said, “Go, sacrifice to your God in the land.” And Moses said, “It is not right to do so, for we would be sacrificing the abomination of the Egyptians to the Lord our God. If we sacrifice the abomination of the Egyptians before their eyes, then will they not stone us? We will go three days’ journey into the wilderness and sacrifice to the Lord our God as He will command us.” So Pharaoh said, “I will let you go, that you may sacrifice to the Lord your God in the wilderness; only you shall not go very far away. Intercede for me.” (Exodus 8:25-28) 

Moses explained to Pharaoh that the sacrifices God required the children of Israel to make would offend the Egyptians based on their beliefs and they would possibly stone the Hebrews; so it would be best for them to go make their sacrifice to God outside of Egypt. Many of the animals they would sacrifice are used as gods in the Egyptian culture. 

The Hebrews did not follow the idolatry worship of the Egyptians. The Lord God even explained how foolish idolatry is, "Those who make an image, all of them are useless, and their precious things shall not profit; they are their own witnesses; they neither see nor know, that they may be ashamed. ... And no one considers in his heart, nor is there knowledge nor understanding to say, “I have burned half of it in the fire, yes, I have also baked bread on its coals; I have roasted meat and eaten it; and shall I make the rest of it an abomination? Shall I fall down before a block of wood?” (Isaiah 44:9-20)

Then Moses said, “Indeed I am going out from you, and I will entreat the Lord, that the swarms of flies may depart tomorrow from Pharaoh, from his servants, and from his people. But let Pharaoh not deal deceitfully anymore in not letting the people go to sacrifice to the Lord.” So Moses went out from Pharaoh and entreated the Lord. And the Lord did according to the word of Moses; He removed the swarms of flies from Pharaoh, from his servants, and from his people. Not one remained. But Pharaoh hardened his heart at this time also; neither would he let the people go. (Exodus 8:29-32)

Why would Moses continue to ask the Lord to remove the plagues and why would the Lord do it before letting the children of Israel leave first?  As the Lord God proclaimed, "...I may lay My hand on Egypt and bring My armies and My people, the children of Israel, out of the land of Egypt by great judgments. And the Egyptians shall know that I am the Lord, when I stretch out My hand on Egypt and bring out the children of Israel from among them.” (Exodus 7:4-5)

He was not just proving Himself to the Egyptians and the rest of the world, but He was also proving Himself to the children of Israel. Remember He told Moses, “I am the Lord. I appeared to Abraham, to Isaac, and to Jacob, as God Almighty, but by My name Lord [JEHOVAH] I was not known to them." (Exodus 6:2-3) In order for the children of Israel to believe and follow Moses, they were going to have to believe he was truly sent by and representing the "I AM THAT I AM"! (Exodus 3:14) But for now the Lord God would continue hardening Pharaoh’s heart, and multiply His signs and His wonders in the land of Egypt... (Exodus 7:3)