"These two verses are considered by many commentators as redundant or misplaced. But they can easily be explained as a summary and epilogue of the Section of the Plagues. [source][source][source]
"In the following section not only the course of events will change, but also the background and the dramatis personae. Till now the central theme was the negotiations conducted by Moses and Aaron on the one hand, and Pharaoh and his servants on the other, in Pharaoh"s palace or its environs. But henceforth the principal hero of the drama will be the people of Israel in its totality, and the perspective will be enlarged. Moses and Aaron will no longer be sent to Pharaoh but to the Israelites, in order to prepare them for the exodus and to implement it; nor will they be enjoined again to perform acts for the purpose of bringing the plagues, for the last plague will take place of its own accord, through the instrumentality of the angel of the Lord. Since the episode about to be narrated represents a new theme, and one, moreover, of fundamental importance, it is desireable [1] that before reading this account we should look back for a moment, and review generally the events that have taken place thus far, as well as the situation obtaining at the conclusion of those events. This review is provided for us in the verses under consideration." [2][source]
The theological lesson that Pharaoh and the Egyptians were to learn from this plague was that Yahweh would destroy the gods that the Egyptians" gods supposedly procreated. Pharaoh was a god and so was his first-born son who would succeed him. The Egyptians attributed the power to procreate to various gods. It was a power for which the Egyptians as well as all ancient peoples depended on their gods. By killing the first-born Yahweh was demonstrating His sovereignty once again. However this plague had more far-reaching consequences and was therefore more significant than all the previous plagues combined. [source][source][source]
"Possibly no land in antiquity was more obsessed with death than Egypt. The real power of the priesthood lay in its alleged ability to guarantee the dead a safe passage to the "Western World" under the benign rule of Osiris. This terrible visitation which defied and defies all rational explanation, showed that Yahweh was not only lord of the forces of nature, but also of life and death." [3][source]
". . . it is by means of the account of the last plague that the author is able to introduce into the Exodus narrative in a clear and precise way the notion of redemption from sin and death. The idea of salvation from slavery and deliverance from Egypt is manifest throughout the early chapters of Exodus. The idea of redemption and salvation from death, however, is the particular contribution of the last plague, especially as the last plague is worked into the narrative by the author.... [source][source][source]
"By means of the last plague, then, the writer is able to bring the Exodus narratives into the larger framework of the whole Pentateuch and particularly that of the early chapters of Genesis. In the midst of the judgment of death, God provided a way of salvation for the promised seed ( Genesis 3:15). Like Enoch ( Exodus 5:22-23), Noah ( Exodus 6:9), and Lot ( Exodus 19:16-19), those who walk in God"s way will be saved from death and destruction." [4][source]
This tenth plague brought Yahweh"s concentrated education of both the Egyptians and the Israelites to a climactic conclusion. [source][source][source]
"In short, therefore, what were the essential purposes of these ten plagues? First of all, they were certainly designed to free the people of God. Second, they were a punishment upon Egypt for her portion in the long oppression of the Hebrews [5]. Third, they were designed to demonstrate the foolishness of idolatry. They were a supreme example both for the Egyptians and for Israel. It was by these that Jehovah revealed His uniqueness in a way that had never before been revealed ( Exodus 6:3; cf. Exodus 10:2). Finally, the plagues clearly demonstrated the awesome, sovereign power of God. In the Book of Genesis , God is described as the Creator of the heavens and the earth and all the laws of nature. In the Book of Exodus the exercise of that creative power is revealed as it leads to the accomplishment of divine goals. God"s sovereignty is not only exercised over the forces of nature, but is also revealed against evil nations and their rulers." [6][source]