What did God tell Abraham to do when He called him out of Ur?
God told Abraham to leave the city of Ur, leave his family, and go to a place that God would show him. Abraham believed God, and that belief became faith; Paul later uses Abraham to show that righteousness was declared only because he believed God.
Les teaches that Abraham was steeped in idolatry as a young man in the city of Ur. God reached down in grace and told him to leave the city, leave his family, and go to a place He would show him, and Abraham believed God. Les draws a contrast between believing God, which becomes faith, and merely believing in God, which is only recognizing that He exists but not having anything to do with Him. Then in Romans 4:5, Paul builds his case that Abraham was declared righteous only because he believed God.