In this chapter, three more plagues are released over Egypt.
This chapter is a direct continuation of the prior chapter, as we see a steady escalation in the ferocity of the plagues, the decimation of Egypt and the stubborn resistance of Pharaoh, even though he appears to waver several times.
The LORD continues to express his divine sovereignty over the realms of creation by releasing frogs from the water realm and covers the land with gnats and flies. It's interesting that no plague strikes the birds, probably because birds have fallen out of human dominion and are not part of Egyptian society/economy.
The magicians replicate the plague of frogs, but their power falls apart at the plague of gnats. At that point, they proclaim that "this is the finger of God". From then on, it no longer says that the magicians try to replicate any of the plagues. The plagues continue to escalate in severity, and the magicians now know that they are facing a power greater than their own. The contest between the magicians and Moses/Aaron is over, but the contest between Pharaoh and God continues.
Starting with the plague of frogs, Pharaoh begins a long pattern of waffling in his resistance. He agrees to let the Hebrews go, and then changing his mind when Moses has the plague removed. He does the same with the plague of flies, agreeing to let the Hebrews go, and then changing his mind when Moses prays the plague away. From my perspective, this behavior is quite peculiar. You would imagine, after seeing the previous plague, that Pharaoh would be convinced, "If they can cover the land with frogs, they can probably cover the land with much more horrible things if I continue to resist," and yet he continues to resist anyway. I'm not sure whether this should be properly ascribed to avarice (the wealth gained through the Hebrews' labor) or pride, refusing to let the Hebrews go out of a sense of superiority, or whether from the emotionally hardening influence of the LORD. While this behavior certainly paints Pharaoh in a negative light, we never really got to see what raised him up into this pattern, much like Abraham and Joseph before him. In their cases, we saw them introduced into the story from a position of faith in God. With Pharaoh, he is first introduced into the story from a position of hostility towards the Hebrews and ignorance and hostility towards God. On the one hand, we know that Pharaoh is responsible for running the most powerful kingdom on earth, and as we saw, his predecessor initially enslaved the Israelites out of fear that they would betray the Egyptians in some war. So it was a political calculus that brought the Israelites into slavery. After that it says that the Hebrews built Pithom and Raamses, so there is a clear economic motivation here as well. But on the other hand, allowing the Israelites to leave would clearly resolve the political risk because they wouldn't be present to undermine the Egyptian military position. This leaves the possible economic motivation of holding 2 million slaves. However, the economic motivation is clearly undermined by the massive devastation of the various plagues, which target the Egyptian economy and which Pharaoh is now witnessing. In conclusion, unless Pharaoh has some reason for believing that the plagues will stop, his behavior is simply not rational. The devastation they are suffering overshadows any possible gain.
In light of that, Pharaoh's true motivation is (in my opinion) fairly inscrutable. We don't know his history and we can largely discount any rational economic or political motivation, which basically leaves irrational or emotional motivations, and Pharaoh's surprising resilience to letting the Hebrews go shows that he has such motivations in good measure. My best guess is that his motive is pride, a sense of superiority over the Hebrews whom he holds in contempt, such as we saw in chapter 5.
We also see for the first time Pharaoh's suspicion that the Israelites will try to escape if they are allowed to go into the wilderness in verses 25 through 28. First he insists they sacrifice "within the land", and then he says they can go out of the land, but "only you shall not go very far away." So Pharaoh seems to doubt if the Israelites will return to their bondage if they are freely allowed to leave, and in this he is quite correct. We have already seen that the LORD is only using this "festival" as an excuse or a deception for their departure from Egypt and return to the promised land, and I have already said I don't know why God felt that this deception was necessary. From my perspective, the raw power of the plagues appears sufficient to make an arbitrary demand of Pharaoh and he should be willing to accede. I also spent quite a bit of Genesis rebuking various characters for their deceptions (Jacob being the foremost deceiver), and yet now God commands Moses to perform this deception. Perhaps someone wiser than myself has a good explanation for what's going on here. Given Pharaoh's skepticism, maybe it was generally understood that the Israelites would not come back and therefore nobody is being deceived? I don't know.
We also see some evidence of religious discord between the Israelites and the Egyptians. Moses states, without explanation, that "we will sacrifice to the LORD our God what is an abomination to the Egyptians." In this matter, Pharaoh does not contradict Moses's assertion and concedes that Moses and the Israelites should go out of Egypt, but "only you shall not go very far away." So some unstated characteristic of Hebrew worship or sacrifice is detestable to the Egyptians. This certainly fits in with other things we have seen before (in Genesis, the Egyptians refused to eat with Hebrews, and we know that the agrarian Egyptians hated the pastoral Hebrews), but it shows that the divisions were also religious in nature, as well as cultural. In light of this general acrimony, the prior enslavement of the Hebrews is perhaps not entirely surprising and their soon departure from Egypt is quite timely.
Some people try to construct a narrative out of the plagues, like that the plague of blood causes all of the frogs to leave the waters, and then the plague of frogs dying causes the plague of flies (i.e. that the plagues are an etiological myth for some drought or famine or something of that kind). This makes some sense with the plagues we've seen so far, but in my opinion it falls apart later on, it's not clear to me how a famine can cause darkness in the sky. But maybe it relates to a volcanic eruption, which poisons the water and darkens the sky, etc? This explanation may present an interesting viewpoint, but it doesn't really have any theological or historical significance to me, so I don't think it's worth spending much time on. Also, this sort of etiology is highly speculative, since there is no historical or textual basis for it.
In my opinion, the most important thing about this chapter is that it introduces what I call the Goshen Principle. The Goshen Principle is simple to explain, but it has some subtle ramifications. Verses 22 and 23 say, "But on that day I will set apart the land of Goshen, where My people are living, so that no swarms of flies will be there, in order that you may know that I, the LORD, am in the midst of the land. I will put a division between My people and your people. Tomorrow this sign will occur." So the Goshen Principle, at the simplest level, is that when God brings a judgment on some people, city or region, the people of God are spared and protected from it.
We have already seen the Goshen Principle in action, though I didn't call it by that name, when in Genesis 19 God sent the two angels to rescue Lot from the soon-to-be-destroyed city of Sodom. Before that, in Genesis 18, Abraham was pleading on behalf of the righteous who live in Sodom, and God was even willing to spare the entire city (both wicked and righteous) if there were found 10 righteous men within it. Since that did not happen, God still sent the two angels who rescued Lot and his family, even though the city was to be destroyed. One presumes that there were no other righteous men in the city.
In this case, the region of Goshen is populated by the Hebrews and therefore the entire region is spared from the plagues that strike the rest of Egypt. Several of the later plagues also note that Goshen was not harmed, and in the final plague, the Hebrews are "passed over" and spared from the deaths of their firstborn in a climactic manifestation of the Goshen Principle. There are several plagues where it does not explicitly state that Goshen was passed over, but my opinion is that Goshen was protected in some fashion from these plagues also, because as we have seen many times, the omission of a statement does not necessarily indicate the contrary. And in this case, the Goshen Principle is so widespread in both the OT and the NT that I don't think it's a stretch at all to consider it universally true even when it's not specifically stated.
The Goshen Principle has some important implications in a variety of areas, perhaps the most commonly discussed being eschatology and the so-called Tribulation. But I don't think that's the most important application, as the Goshen Principle is relevant to many areas of the bible and to modern life. The Goshen Principle, stated generally, means that those who follow God receive a sort of divine protection from harm, especially with respect to God's judgment of wickedness. This doesn't mean that nothing bad ever happens to true followers of the LORD (the enslavement of the Israelites is enough proof of that), but it does mean that they are not recipients of judgment, for the simple reason that God does not hold them guilty of whatever crimes are being punished. I also think that believers have a sort of protection even against the hostile actions of other people or natural conditions. We saw that God threatening Laban when he was going to harm Jacob (Gen 31:24), God allowed Isaac to reap 100-fold in the face of a regional famine (Genesis 26:12) and God gave Joseph a divine providence so that he was able to rise in power multiple times during his life, ending as the vice-ruler of Egypt. The Goshen Principle is an extension of all of these prior events and is simply another form of divine protection for God's chosen people as it pertains to divine judgment.
Lastly, note that Exodus never says that the prior plague, the plague of blood, ceased. The plague that followed it, the plague of frogs, says "the Nile will swarm with frogs." Since we previously saw the Nile filled with blood and all the fish dying, I'd say this strongly implies the Nile (and associated rivers, streams, ponds, etc) are now habitable, i.e. drinkable water. While one could say that the frogs came out of the streams and the Nile because of the plague of blood, the text implies a gap of at least 7 days between the blood and the frogs, which makes this view somewhat less likely. There are a few other plagues which are not specifically called off. In this chapter, we see the plague of gnats is never explicitly ended. I don't think it's unreasonable for some commentators to say that the plague simply didn't end, but I find it more likely that the plague (of blood, gnats) ended and the author of Exodus simply didn't think it was important to tell us. This would be consistent with the many other things that we are not told, but are forced to presume at various times for various reasons. So while it's reasonable to say that there's some overlap between the plagues, some of the plagues end without us being told. For most of the plagues this isn't important however, because Moses prays for the majority of the plagues to end, just like he does here for the plagues of frogs and flies.