This chapter begins with God stating that he is performing the miraculous plagues to create a legend for the Hebrew generations and so that the Hebrews (and presumably the Egyptians) might believe in God.
The threat of a locust invasion brings Pharaoh's officials to the brink of rebellion and Pharaoh to the brink of giving in. Apparently, thinking Moses will take just the men, Pharaoh says "The Lord be with you," then abruptly reverses himself on considering that if the Hebrews take their children and wives, as well as their herds, they might well not return. This plague apparently does not spare the Hebrews.
Locusts are a prominent feature of the prophets, notably the book of Joel. They also appear in Revelation.
Perhaps there should be an asterisk attached to the Lord's command to Pharaoh, "Let my people go." When the plague of darkness descends, Pharaoh is willing to let the human beings, but not their livestock, leave This offer is refused as inadequate, since without livestock, the Hebrews would be unable to offer sacrifices to the Lord. The final plague, that of darkness, affects only the Egyptians.
Torah commentary on the darkness "that one can feel," which the Lord commanded, is as follows:
The rabbi said, "This darkness from which the Egyptians suffered was a very special kind of darkness. It was not a darkness that stopped the eyes from seeing. Rather, it was a darkness that affected the heart. If they were not able to see physically, these Egyptians were not able to feel for each other, nor to care for the well-being of each other. This is exactly what the Torah means when it says: 'They could not see one another.' They were blind to the needs of the other. Each person saw only himself or herself, and that, my young friend," said the rabbi, "is a terrible plague." (
http://www.templesinaino.org/s011003.htm).
Other Torah commentary suggests that most of the Hebrews died during the plague of darkness (
http://www.jewishgates.com/file.asp?File_ID=1024,
http://www.yashanet.com/shabbat/parsha/bo.htm) This does not seem to correspond with the text, which says that the lights remained on for the Israelites.
Moses' response to Pharaoh's subsequent command to leave and never return is one with many meanings. The Hebrew word
ken is elsewhere translated variously, "It was so," "therefore," "loyal," "according to your words," "the more," "according to your words," and so on. At any rate, by Pharaoh's command, he takes personal responsibility for the departure of Moses and, with him, the Hebrews.