Genesis 15:6 And Abram believed the Lord, and the Lord counted him as righteous because of his faith.
7 Then the Lord told him, "I am the Lord who brought you out of Ur of the Chaldeans to give you this land as your possession."
8 But Abram replied, "O Sovereign Lord, how can I be sure that I will actually possess it?"
God made some wonderful promises to Abram for his life and the lives of many descendants to follow him. Abram believed God and as a result God chalked up righteousness to Abram's account. But Abram needed some assurance. This is true today, as well, in our walk with God. He makes promises to us for life, for forgiveness, for eternal life. When we believe God's word we are counted righteous...but we may still need assurance of that. And, just as God provided that assurance to Abram through the story that follows these verses, so He still provides that assurance today.
Romans 4: 22 And because of Abraham's faith, God counted him as righteous. 23 And when God counted him as righteous, it wasn't just for Abraham's benefit. It was recorded 24 for our benefit, too, assuring us that God will also count us as righteous if we believe in him, the one who raised Jesus our Lord from the dead. 25 He was handed over to die because of our sins, and he was raised to life to make us right with God.