Genesis 15

1 Abraham was afraid that the armies he had just defeated would rise again to attack him. God calms Abraham's fears with a promise to protect him. When God protects us, we have nothing to fear.

Notice that God said that He was Abraham's great reward. He is the source of every blessing. When we have faith in God, He gives us of Himself. He is good, and He is love. What more could we possible want?

2 Many years earlier, God promised that Abraham would become a great nation (Gen 12:7). Abraham already had wealth and did not need any physical possessions. What he wanted most of all now was a son. This seemed hopeless since both he and his wife were old.
3 It was customary for a man without a son to make his head servant his heir (mentioned in the Nuzi Tablets).
4 God assures Abraham that his servant will not be his heir. God confirms that Abraham will have a son to inherit both his possessions and God's promises.
5 Very few people take the time to count the stars. The unaided eye can see approximately 10,000 stars. Obviously, Abraham had more descendants than that. The idea is that there will be so many descendants that they would be practically innumerable.
6 Abraham simply believed that what God said was true. It was his faith in God, not any religious ritual, that made him righteous in God's eyes. Gal 3:6-14 shows that all who believe in God are Abraham's descendants through faith. Thus, anyone can share in the promised inheritance that will be realized upon Jesus' return.
12 God showed Abraham the future. It would not be pleasant for his descendants, and he shared their pain during the vision.
13 God foretells the enslavement of the Israelites by the Egyptians.
15 Abraham would not personally see the terror that was to befall his descendants.
16 The Amorites did not believe in God, and their religious practices were revolting to Him. He would give them an additional 400 or so years to repent, but instead they would become further hardened. By the time the Israelites left Egypt, the Amorites would be beyond hope to repent. Therefore, God would be justified to destroy them, just as He was justified in destroying the hopeless pre-flood world.
17 In Abraham's day, a solemn covenant was ratified with this unusual ceremony. One or more animals were cut in half and the two agreeing parties would walk between the halves. Here, we see only God symbolically moving between the pieces. This is because the covenant was one that only God could keep. Only by His actions would the Israelites be freed from Egypt and brought to the Promised Land.
18 The Israelites were promised a great deal of land.
19 The Israelites would displace and destroy the current inhabitants of the land.