Abram seems to be having a bit of a faith crisis here. After many years of struggling with infertility, he is questioning how God is planning to give him many descendants. God reassures Abram that he will keep his promise. We are told that Abram believed God, so God considered Abram righteous. This verse is referenced in Roman 4:3, 22 and 23 and Galatians 3:6 to show us it is faith that makes us right with God, and James 2:23 tells us faith also leads to righteous living. The ceremony of God passing between the halves of the dead animals symbolizes that God would have to die like these animals before it would be possible for God not to keep His promise. This event describes a pretty strong promise! It shouldn’t have been necessary for God to confirm his promise this strongly, but God meets Abram in his weakness.
Here and in chapter 12, we see Abram struggling with his faith and at other times being strong. Everyone’s faith is sometimes weak and sometimes strong, but God always remains faithful. Faith is the first step in entering into a relationship with God, but that doesn’t mean our faith never wavers. If a person wants to stay close to God, that person needs more faith.