And the Lord said unto Moses, Stretch out thine hand toward heaven that there may be darkness over the land of Egypt, even darkness which may be felt. Without previous announcement or warning this plague came upon Egypt as another sign of God's almighty power. It was a supernatural, miraculous darkness, so heavy that all light from whatever source was cut off completely and all men were reduced to the necessity of feeling their way.
Related Commentaries of Exodus 10:21
Exodus 10:21
21 And the LORD said unto Moses, Stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt.