Torah is not in heaven – it is in your mouth and in your heart to do it. Ibn Ezra explains the heart is essential for Jewish practice.
God gives Moses a mission – save the Israelites from slavery. When Moses worries about his speaking ability, God gives him a spokesman, his brother Aaron.
The Israelites constantly complain in the wilderness. In the aftermath of Korach’s rebellion, the people complain yet again. Rashbam explains their reason.