The ninth plague, of darkness, is extremely telling. According to Midrash, the Egyptians could not see everything but the Israelites, in their neighborhood of Goshen, had full access to light. This was an all-consuming darkness, where “people could not see one another and for three days no one could get up from where he was.” The medieval commentator Nachmanides describes the darkness as a fog-like condition which extinguished all flames. Ibn Ezra said it was so dark that the Egyptians could not even keep track of the passing days.
The Etz Chaim Chumash challenges the idea that this was a physical darkness, as why then would the Egyptians not light candles? It comments that perhaps it was “a spiritual or psychological darkness, a deep depression.” After all, this is the ninth plague that has befallen the Egyptians, and it is one that attacks the sun, which they worshipped. Perhaps the Egyptians no longer believed there was hope for a better future, so why bother doing anything?
In such a condition of fogginess, confusion and depression, it was the perfect opportunity for Israel to enter into armed rebellion against the Egyptians or at least steal all of their belongings. However the Israelites did neither of these, instead leaving the Egyptians and their property untouched.
When one is vulnerable, surrounded by complete darkness, s/he realizes the kindness of others. As Samson Raphael Hirsch points out, this led the Egyptians to willingly give the Israelites their silver and gold during their exodus. It also led to some of the Egyptians joining with the Israelites in leaving Egypt. These Egyptians saw that because the Israelites left their belongings alone during a time of vulnerability that this was a trustworthy people who they could join, as opposed to staying in a harsh, Egyptian society.
This illustrates a core teaching of Judaism. As Jews we are not supposed to take advantage of the misfortunes of others, especially when they did not provoke the situation. The plagues were meant to be primarily against Pharaoh, to show him who G-d was, yet they affected all of the Egyptians. Our ancestors recognized that the plagues falling on the Egyptians did not give them the right to “run amuck” and plunder their belongings. It would have been enticing for a slave to turn on his master at the slightest opportunity, yet the Israelites understood that the plagues were there for a higher purpose, to demonstrate the power of G-d.
There are times in each of our lives at which we might feel schadenfreude, pleasure in the pain of someone else, especially if that person has exploited or taken advantage of us in the past. It is tempting to descend on him/her at this moment of great vulnerability. Our ancestors understood, however, that this human temptation was not something to embrace. The Egyptians were suffering enough from G-d, and our ancestors would soon be free from their tyranny. The compassion that they showed the Egyptians during this time would not go unnoticed. Perhaps our ancestors were starting to learn what it means to be a people of G-d: to show compassion and mercy to those who are in a weaker state, even when one can make a valid argument to do otherwise. May we learn from their example and make it our own.
 Exodus 10:23
 Etz Chaim Chumash, Page 377, note 23