Over and over, though he wants his people to be free, God hardens Pharaoh's heart so that he won't let them go. In the same way, the Spirit of God so arranges things that our own efforts at holiness and freedom from sin are frustrated, until we learn to rely on God alone.
God does not invite us to leave the slavery of Egypt; we are commanded to do so! But it's not a project that God gives us to do by ourselves. We have no army, no force of our own. And God will see to it that any human effort to save ourselves will come to naught.
When God commands us to leave our slavery behind, it is not exactly a task to be accomplished. The task is to accept the liberation that only God gives, to allow ourselves to be caught up in the salvation that God is working.
So if we spend our time trying to get Pharaoh to let us go, we're doomed. Salvation is for the glory of God. And God is jealous of his glory, and will never let Pharaoh get any credit for our salvation.
Lent is, in part, the time to prepare ourselves for the renewal of our baptismal vows at the great Vigil. To pass again through the Red Sea and out of the slavery of Egypt. But this is always God's work, not ours.
Grace might be free, but it ain't cheap.