Why did God choose Moses to save Israelites who were enslaved?

It was mentioned in Exodus that God has granted Moses abilities such as turning his staff into a snake and turning the water of the Nile into blood in order to make the people believe he was sent by God. Why had God not by himself saved the Israelites from slavery? Why did he not talk to them? “But I will harden Pharaoh’s heart, and though I multiply my signs and wonders in Egypt,” why did God harden pharaohs heart and torment the Israelites more?