In Exodus 10, Moses records that God gave him a purpose for his recurring face-to-face meetings with Pharaoh: that you may know that I am the LORD (v. 2). If one reads while on autopilot at this point, a major idea will fly right by, missed and unappreciated.
Often, when dealing with the plague narratives, the preacher or teacher has grown tired of saying the same things about God’s power, his might, and his sovereignty over nature in the plagues. Treatment of the first few plagues receives plenty of coverage, and the farther into the narrative one goes, the quicker he desires to move through the plagues. After all, most people are familiar with what God is doing. Whether we admit it or not, we often skim narratives like these because we think God is basically doing the same thing in a different way. We do this with the Gospel narratives and the events in Acts as well.
However, when skimming, we miss words the Holy Spirit had someone put to paper for our growth and rootedness in Christ. Here, God provided a purpose statement for his display of power over Pharaoh, the Egyptians, and their pagan gods. That purpose, however, is not the liberation of the children of Israel from slavery. Instead, it is that they know him. To be sure, God sent Moses to lead his people away from bondage in a foreign land to the land promised to Abraham (Exodus 6:8). The entirety of the narrative of Exodus 5-14 reveals God as desiring himself to be known throughout the land of Egypt. 
It would be easy to try and understand this passage from Exodus by dwelling on just how many locusts there were, or what a “darkness which may be felt” is (v. 21). In the modern West, great difficulty presents itself when we try to understand such things. We don’t deal with locusts, and most of us aren’t completely reliant on agriculture the way the people of Exodus 10 are. We might look up videos of locusts online (I did), but the problem is this: in an age where Iron Man can fight aliens on a movie screen on-demand, there’s nothing that wows us about seeing a bunch of grasshoppers flying around. Artificial light has been around long enough that, save spelunkers, we have no idea what inky darkness truly is.
We might also look into the assertion of the sovereignty of the LORD over the crops of Egypt and the sun. These are both big deals, to be sure. Nearly every ancient culture had several fertility deities (Baal was one of these), and Egypt was no exception, having several. No fertility god or goddess was going to overcome the LORD in preserving what remained of Egypt’s farms after these locusts came through. Furthermore, the sun held a special place in Egypt’s religion. Even when one king attempted to make Egypt a monotheistic nation, the chosen one god of the land was still the sun. These gods are shown to be no-gods in Exodus 10.
However, the point is this: that God’s people would know him and would recount his actions to their children and grandchildren. More important than the defeat of the false gods is the revelation of the true God, the LORD. It is not just that God knocked the stool from beneath the Egyptian pantheon, including Pharaoh, but that he revealed himself to be the true ruler of the land the Egyptians thought of as their own. Rather than leaving anyone to guess at why the plagues had arrived, God also chose to reveal himself by giving Moses and Aaron words to say about him. Uniting action and word, the people were to then recount these events to those not yet born that they also would know God. We are doing this even today, as you read this blog. The actions of God happen in space and time, but his desire is that they be spoken of to others in other spaces throughout time. The purpose of these plagues is evangelistic: that your children and grandchildren would also be followers of the God who revealed himself in his control over all of nature in Egypt.
As we talk to our children and grandchildren about the various false gods of our world, be those greed or laziness or even the myriad forms of illicit sex that our culture had commodified, it’s not that we’re merely trying to get them to avoid sins that they would live publicly moral lives. It’s that we want to reveal those gods for what they are for the purpose that our children and grandchildren would know and follow after the true God, the one who became the man Jesus Christ.
W. Ross Blackburn, The God Who Makes Himself Known: The Missionary Heart of the Book of Exodus, vol. 28 of New Studies in Biblical Theology, ed. D. A. Carson (Downers Grove: InterVarsity Press, 2012), 41.