What does Exodus 10:21 mean?
This begins the description of the ninth plague on Egypt (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24; 10:14). Earlier disasters challenged the idea that Egyptian idols had power over those aspects of the world. Deities such as Khnum, Heqet, Hapi, Wadjet, Hathor, Apis, Isis, Sunu, and Sekhmet were proven impotent when the God of the Hebrews controlled things like the Nile, animals, or disease. This plague strikes at one of Egypt's most important idols: Ra.Ra was the Egyptian god of the sun. Egypt's kings, called pharaohs, were supposedly descendants and manifestations of this deity. Not only will the Lord bring darkness, but an extreme darkness: something so deep that it is poetically described as "felt." Days of continual, absolute darkness (Exodus 10:22) directly counter the claim that Ra controlled daylight. By extension, this also dismissed the idea that Pharaoh was somehow divine. To make the message especially clear, this darkness will not affect the lands where Hebrew slaves live (Exodus 10:23).
In Scripture, light is a metaphor for truth, wisdom, and God's goodness (Psalm 27:1; 119:105; Matthew 4:16). Darkness and blindness are often used in reference to spiritual separation (2 Corinthians 4:4; 1 John 1:5) and divine judgment (Proverbs 4:19; Ezekiel 32:7–8; Revelation 16:10). Symbolically, this plague demonstrates that Egypt is in rebellion against God.