Another matter, “it was when Pharaoh let [the people] go” – when Pharaoh let the people go, who shouted woe? It was Pharaoh. It is analogous to a king whose son was going to a certain province. He went and stayed with a certain wealthy person.
The wealthy person received the king’s son generously. When the king heard who had received his son, and in what province he was, he sent a letter to that man and said to him: ‘Send my son [to me.’ He sent this letter] once, twice, three times; he would send all the time, and each and every hour, until he went and took his son himself. That man began shouting because the king’s son left his house.
His neighbors said to him: ‘Why are you screaming?’ He said to them: ‘I was honored when the king’s son was with me, as the king would write a letter to me, and he needed me, and I enjoyed his respect. Now that the king’s son has been taken from me, he does not need me for anything. That is why I am screaming.’
So, too, Pharaoh said: ‘When Israel was with me, the Holy One blessed be He needed me, and I enjoyed His respect. He would send me a letter all the time, and say: “So said the Lord, God of the Hebrews: Let My people go”’ (Exodus 9:1). Pharaoh would hear from Moses: “Let My son go,” but he did not seek to let them go. When the Holy One blessed be He descended to Egypt and took Israel out, as it is stated: “I descended to deliver it from the hand of Egypt” (Exodus 3:8), Pharaoh began screaming: ‘Woe is me that I let Israel go’– therefore, it says: “It was [vayhi] when Pharaoh let [the people] go.”