Every Christian has a choice – to continuing following God, or to go back to a life of sin and death. Joshua leads the people of Israel in a renewal of their commitment to follow God, and only God.
Moses was scared to lead God's people. He knew he couldn't do it. But God had the answer for him, and for us too when we're scared to live for God: I AM, that great and powerful, living and eternal God who sends us, goes with us.