For 400 years Egypt had ‘humbled’ Israel (Gen 15:13) – ie they had afflicted and impoverished them. Moses, at the head of this afflicted people became the most humble man on earth (Num 12:3). He is therefore the polar opposite of Pharaoh – one raised up before all the earth (Ex 9:16) and who “refuses to humble himself before the LORD.” (Ex 10:3)
This is what the plagues are for - humbling.
In Amos 4 we see plagues falling on Israel (in fulfilment of the warnings against covenant breaking in Deut 28:59) and the constant refrain is - "yet you have not returned to me."
"I sent plagues among you as I did to Egypt… yet you have not returned to me," declares the LORD. (Amos 4:10)
Again when the plagues fall on the whole earth in Revelation 15&16 (which I take to be the time between ascension and second coming, i.e. now) the Holy Spirit laments "but they refused to repent and glorify God." (Rev 16:9)
You are either humbled or hardened by these plagues (see here for how Pharaoh's hardening develops). First in the land of Egypt, next with the nation of Israel - summed up in the true Son who was humbled at Calvary, then (judgement beginning from the house of God, 1 Pet 4:17) it flows out to the whole world. The very same plagues fall and for some they humble, for others they harden.
And we definitely want to be on the humble side. (Ps 25:9; 37:11; 76:9; Isaiah 11:4; 61:1):
“He mocks proud mockers, but gives grace to the humble” (Prov 3:34; James 4:6; 1 Pet 5:5)
“The LORD lifts up the humble, He casts the wicked to the ground” (Ps 147:6)
“For the LORD takes delight in his people; he crowns the humble with salvation.” (Psalm 149:4)
“Seek the LORD, all you humble of the land, you who do what he commands. Seek righteousness, seek humility; perhaps you will be sheltered on the day of the LORD's anger.” (Zephaniah 2:3)
In Exodus, the humbling plagues increase until the climax where it requires a literal sheltering under the blood of the lamb.
For Israel, the plagues that fell on Egypt will judge the people of God (Amos 4-5) and there can be no escape. (That should really shock us - Israel becomes Egypt!). There will be a top-down judgement that begins with the true Son, the true Priest, the true King and Most Humble of Men (Dan 4:17). Christ will be eaten up by ravenous enemies (Ps 22:13) and 'perish' in the darkness (Luke 23:44f). This is most shocking of all - Jesus, the Son of God becomes like the son of Pharaoh - slaughtered, devoured, perishing in the darkness.
For us, plagues are falling on Babylon which affect the whole world (Rev 15-16). And the only place of shelter is under the altar (Rev 6). In this way we become the humble, taking refuge in the Son (Ps 2:10-12).
In Exodus 10, the locusts are described simply as "this death" by Pharaoh. They devour (v5,12) - like hostile armies (Deut 28:52f; Joel 2:25; Nahum 3:15f), like the sword (Deut 32:42) like Satan (1 Pet 5:8), and like the grave itself (e.g. Num 16:32).
Egypt perishes (v7) at the hand of the LORD.
Without warning the darkness follows hard on the heels of the locusts. This is the first time this kind of darkness has been mentioned since Genesis 1. There we encountered the primeval darkness associated with "the deep" and "the waters". Only by the power of the Word is light separated from darkness. Again in Exodus 14:20 we will see the Word - the Mighty Angel - separating light from darkness.
But without this great Light of the world, there is only darkness. "Felt darkness" (10:21) which might simply mean darkness that makes you grope. And calamitous darkness (10:22) which is so much associated with the day of the LORD.
The hardness and madness of Pharaoh is seen in his driving Moses away (v28) - btw does anyone have any thoughts on the parallel between 10:28 and 33:20?
Pharaoh rejects the Priest who has been praying for him, forgiving him and standing between him and the judgements of God. He wants to be left alone in the darkness. This is such a powerful picture of humanity opposing Christ. Even in calamitous darkness we drive Christ away to be left alone in our sin (John 3:19f). And God always gives people what they most want. Even in judgement, He only hands people over to what their hearts actually desire. And so with his priest and intercessor rejected, Pharaoh and his people await their fearful and certain judgement.