The slow process of getting Pharaoh to change his mind and let the people go continues.
There are two overriding issues. Why does the process take so long, with so many false hopes and miracles that failed to have the desired impact, and why does it take so long for Pharaoh to change his mind?
Every process in the Torah takes time. God may make promises, humans may make resolutions, but the world of human interaction is one where immediate results are rarely achieved. Relationships take time to develop, good ones and bad ones.
God tries different ways of impressing Moses at the Burning Bush–fire, snakes, leprosy, and then rational argument. Similarly, Moses tries a series of ways of trying to persuade the greatest most powerful king on earth that a small, God-inspired nation should be taken seriously. It is a game of trial and error. At first Pharaoh is dismissive; then he begins to wonder. He half relents, but with conditions attached. His advisors wilt first and they try to persuade him to let the Israelites go. The campaign is waged against every level of Egyptian society with the aim of getting them to realize that there is something here to be taken seriously. And then it is too late. This is how we humans function. We think we can cope. We disregard the warning signs. And then wham.
And into this whole story of human reactions to disaster comes the legal instruction to keep the Pesach festival. The details of observance seem out of place. Yet it is through daily behavior that we train ourselves and we sensitize ourselves to be conscious of our actions in the hope that this will make us better people. The lesson to be drawn is that foresight, consideration, would have helped Pharaoh and his people. Similarly, they may help us, today, to lead more effective daily lives.