This really is the turning point in Abram's life.... well, the first turning point. :) I guess he has maybe 1-2 more later on. But I see this as the turning point because of the emotional side. Abram just rescued Lot, overpowered four kings and destroyed their army. He turned down the king of Sodom's reward and proclaimed his devotion to the Lord, that he would take the succor of no man and adhere to the Lord in all things. What an oath! This is the consistent pattern we see in Abram's life, and it really is striking. And here, after all that, God speaks to Abram again "in a vision" (again, note the different means through which God speaks to Abram). So this was a vision that Abram saw, and God says, I am your shield and your very great reward. Abram is torn by this. On the one hand, he honors and trusts God, but on the other hand, he still doesn't have a son. So he is torn between the promised heir and the present lack. This is no doubt why Abram is called the father of faith, because he is going through the same experience that so many do, trying to reconcile the promises of God with the present, and waiting and striving for the fulfillment of those promises.
(Eliezer of Damascus is probably Abraham's chief servant.)
Then the word of the Lord comes to Abram again: you will have a son from your own body. And then God takes him outside to count the stars, and that would be the number of his descendants. Abram believes God, and that power of faith is Abram's righteousness. The dialogue continues. God has already promised him this son, and Abram believes, and now God strikes up on the second key element, which is possessing the land. God tells Abram to bring animals for sacrifice, so that they might establish a covenant. This is a peculiar story, because Abram falls into a deep sleep but then a torch and a "smoking oven" pass through the sacrificed animals. I always wondered how would Abram know that they passed if he was in a deep sleep. I'm not entirely sure other than that verse 17 happens after the deep sleep, so possibly it was a deep sleep, God speaks verses 13-16, then Abram wakes up and sees verse 17. Of course, this story is being told by a writer other than Abram, so the author would not have to rely on Abram's first-hand knowledge.
Anyway, God establishes the covenant. The reason for walking through the animals is that you are affirming "If I do not uphold this covenant, I agree that what was done to the animals shall be done to me." So you basically affirm that the other party has the right to kill you if you fail on your end of the agreement.
God's promise is affirmed. Abram believes, in spite of present circumstances, and he becomes the father of faith.