James 2:23, NIV: And the scripture was fulfilled that says, “Abraham believed God, and it was credited to him as righteousness,” and he was called God's friend.

The sin of Adam first and foremost was in this: that although he understood God’s word concerning the tree of knowledge, and knew what God said would be the result of eating from the tree, he chose to believe something else. Adam chose to believe that there was indeed a possibility that God’s word was not good. He believed the lie of Satan, and he acted on that lie. In contrast, we read these words concerning Abraham: that he “believed God, and it was credited to him as righteousness.” People often ask, “What did people in the Old Testament have do to be saved since Jesus had not yet come?” What saved them is what saves us today—faith in God, and taking Him at His word. Abraham trusted God’s word concerning His promises to Abraham and his decedents. Today, we take God at His word concerning our sin, our need for salvation, and the means He chose to bring us salvation through His Son, Jesus. True faith and trust in God is what opens the door for Him to enter into our lives and recreate us in the likeness of His Son.