Exodus 3:11 - Moses: I'm a nobody - God: I will be with you. 

Exodus 3:13 - Moses: I'm not a theologian - God: I AM Who I AM. Tell the people of Israel "I AM sent me to you"

Exodus 4:11 - Moses: I am unconvincing - God: God gives him three miraculous signs to show the Israelites (staff to snake, leprous hand to clean hand, & water & dirt to blood)

Exodus 4:10 - Moses: I am not a preacher - God: I'll be right there with you, give you the words you need

Exodus 4:13 - Moses: I'm not ready, I'm scared - God: I'll send your brother Aaron, who is an eloquent speaker, to be your spokesman

Exodus 3:11-12 

But Moses said to God, “Who am I that I should go to Pharaoh and bring the children of Israel out of Egypt?” 12 He said, “But I will be with you, and this shall be the sign for you, that I have sent you: when you have brought the people out of Egypt, you shall serve God on this mountain.”