Exodus — Chapter 10

The Lord said to Moses: Go in to Pharaoh; for I have hardened his heart, and the heart of his servants, that I may work these my signs in him. Lapide notes that ten plagues are sent—not nine or seven—because ten is the number of the Decalogue: the plagues are in some sense a punishment for the violation of all ten commandments, which Egypt's system of forced labor, idol worship, and oppression embodied.

And thou mayst tell in the ears of thy son, and of thy grandson, how often I have plagued the Egyptians, and what signs I have shewn amongst them: and you may know that I am the Lord. The plagues are designed as catechetical material for all future generations. Lapide notes that God's mighty acts in history are not merely events of the past but perpetually relevant teachings: the meditation on the Exodus forms the spiritual character of every generation that receives it. The Catechism as a genre begins with the Exodus narrative.

The ninth plague—darkness that could be felt (tenebrae palpabiles). Lapide explains that this was not ordinary night but a supernatural darkness produced by God blocking or absorbing light throughout Egypt, while light continued in the homes of the Israelites. He allegorizes: this visible darkness typifies the spiritual blindness of those hardened in sin, while the light in Israel's dwellings typifies sanctifying grace and the light of faith, which alone illumines the soul's interior.

Moses stretched forth his hand toward heaven, and there was horrible darkness in all the land of Egypt for three days. Lapide notes that the darkness lasted exactly three days—a figure, says Origen, of the three days of Christ in the tomb, during which spiritual darkness covered the world before the light of the Resurrection. The darkness that could be felt (tenebrae palpabiles) signifies the palpable weight of sin on the conscience of those who have rejected the light of grace.