And He Believed the Lord
Genesis 15:6 is an important verse; Paul references it both in Romans 4:9 and Galatians 3:6, teaching that faith has always been the only way for sinful man to relate to God.
This is important to grasp. Old Testament believers may have had less revelation than New Testament believers, but they still related to God by faith. Failure to do so was failure to keep the covenant (Romans 9:30-33). The only way to know God, to relate to God, is through faith.