So we can finally start calling Abram as Abraham, as in this chapter, God renames Abram (exalted father) to Abraham (father of many). Seems like a cruel joke to rename a guy who is about to turn 100 and whose wife is on the verge of turning 90. But when God renames someone, it is far from a joke, but rather an assurance of the fulfillment of the promise he had made to Abram almost a quarter of a century ago.
Chapter 15 starts off with God renewing his promise to Abram with the words “I am your shield, your very great reward”. That is what God was offering Abram. In a sense offering himself through the birth of Jesus the snake crusher.
But Abram misconstrues this to mean that God will bless him with great wealth and land and quickly speaks his mind saying that the inheritance that God is promising him in the future is of no use to him without a legal heir. He will surely not be alive to enjoy it and since he does not have any sons (not yet) his servant Eliezer’s family would reap the benefits.