Today's reading, Gen 15:1–21 and Gen 17:1–8, looks at the covenant that God made with Abram. God begins in chapter 15 by promising Abram an heir, his own son. God also promises that Abram's descendants will inhabit the land from the Nile to the Euphrates. God promises Abram that his descendants will inherit the land after a 400 year period as sojourners and servants in a land that is not theirs.
God goes on to make a covenant with Abram. God causes Abram to fall into a deep sleep while God performs act of making the covenant. Why do you think God would have made Abram fall asleep and not pass between the animals as He did? Remember Genesis 8:21.
In chapter 17, God extends the reach of his agreement with Abram. He will not only make Abram an "exalted father", as his name meant, but changed his name to Abraham, meaning "father of the multitudes." Also, his descendants will not only be promised the land for a period of time, but forever. The most significant promise that God made to Abraham is that his descendants will know Him as their God.
Think about the fact that Abraham had to follow God's will and have faith. Yes he stumbled along the way, everyone does. However, it was Abraham's faith that was counted to him as righteousness. Where did Abraham's faith come from?