Exodus 10:21-29

Then the Lord said to Moses, ‘Stretch out your hand towards heaven so that there may be darkness¹ over the land of Egypt, a darkness that can be felt.’²

So Moses stretched out his hand towards heaven, and there was dense darkness in all the land of Egypt for three days.³ People could not see one another, and for three days they could not move from where they were; but all the Israelites had light where they lived.⁴
Then Pharaoh summoned Moses, and said, ‘Go, worship the Lord.⁵ Only your flocks and your herds shall remain behind.⁶ Even your children may go with you.’
But Moses said, ‘You must also let us have sacrifices and burnt-offerings to sacrifice to the Lord our God. Our livestock also must go with us; not a hoof shall be left behind, for we must choose some of them for the worship of the Lord our God, and we will not know what to use to worship the Lord until we arrive there.’⁷
But the Lord hardened Pharaoh’s heart,⁸ and he was unwilling to let them go. Then Pharaoh said to him, ‘Get away from me! Take care that you do not see my face again, for on the day you see my face you shall die.’⁹
Moses said, ‘Just as you say! I will never see your face again.’¹⁰

1 My Study Bible notes that this is a condemnation of the Egyptian sun god, Re

2 Once again a plague without warning

3 The effects of the plague don't sound as bad as previous ones, but the symbolism is striking.

4 Fortunes of the Israelites are once again set apart

5 Once again Pharaoh gives in under destress

6 But Pharaoh can't give in completely – he always has to hold onto some condition.

7 Moses holds strong – he does not want to accept any conditions

8 The initiative for hardening Pharaoh's heart is placed on God once again.

9 What a strong statement from someone who is in such a poor position.

10 Is that a prophecy or just a strong statement?

Take-home: The plagues continue to put fear into Pharaoh, and he is willing to give up more than he has before. But Moses isn't willing to settle for anything less than total freedom for the whole community to worship. This flips Pharaoh back to harsh words of rebuke, setting the scene for the final plague.