It would have been a lot easier on everybody if God had allowed the Israelites to just leave Egypt in the first place. God hardened Pharaoh's heart. Why? God says in the first few verses of chapter seven that he did this so that he could multiply his miraculous signs and wonders.
What is the point? In 7:5, he states clearly his reason: so that the Egyptians "will realize that I am the Lord." The whole point is that God receive glory. If he only wanted the Israelites out, he could have softened Pharaoh's heart from the first petition of Moses and Aaron.
God wants glory. In the work among the Dong people, God wants glory. Who will declare the glory of the Lord? Who is going to sing his praises for the things he does among them? If we do not, the very rocks will do so for us. So, let us save those poor rocks their breath and do so now in honor of the One who is saving them.
Father of all, God, we come to praise you for who you are. You are the father of the Dong people. You have planned their salvation from the beginning of the world and sent your son to verify that promise. You have already begun your work, and though we do not know how you will do it, we praise you for what you have done, what you are now doing, and what you will do to accomplish you purposes among them. May you be praised.