BBC: Genesis 15:4-6
Then the word of the Lord came to him: “This man will not be your heir, but a son who is your own flesh and blood will be your heir.” He took him outside and said, “Look up at the sky and count the stars—if indeed you can count them.” Then he said to him, “So shall your offspring be.”
Abram believed the Lord, and he credited it to him as righteousness. – Genesis 15:4-6
Though the word “in a vision” (Gen 15:1) does not occur here, it can be presumed that this encounter continues in a vision before Abram. The Lord’s response to Abram is important because it is a continuation of God’s declaration as a reward. Abram is seeking one descendent to pass the Lord onto but God will give him many heirs. By this the Lord promises to Abram that He is a reward unlike any other.
Abram’s response to this declaration and promise is faith. This faith brings him into a righteous standing before God. This event is the basis of God’s justification for all people. This is not merely the establishment of Israel but God’s bringing about a people who belong to Him (Rom 3:29-4:3).