The matter of Canaan was settled for Abraham, but from Genesis 15, we see the matter of his son. This does not mean that Canaan is no longer an issue after chapter fifteen. It only means that the focus is no longer on Canaan, but on the seed.
Genesis 15:1 says, "After these things the word of the Lord came unto Abram in a vision, saying, Fear not, Abram: I am thy shield, and thy exceeding great reward."
It was very meaningful for God to reassure Abraham with such a word even though he had just come back from a victory. We have to realize that Abraham was only a man, and his victory was the victory of a man; it was not a superhuman victory. Although God granted him a victory, He did not make him superhuman. It was easy for Abraham to refuse the riches of Sodom when he had the enjoyment of the bread and the wine from Melchizedek; it was easy for him to deny everything then. But after the moment of victory, when the excitement and uproar were over, and when he began to contemplate in his tent, he would undoubtedly worry about how he had offended the four kings by saving Lot, and how he had offended the king of Sodom by declining his goods. It was unavoidable for him to have some fear. We can detect this from God's word to Abraham. God always has a reason when He speaks. God said, "Fear not," because Abraham was afraid. God gave him two reasons to not fear: (1) "I am thy shield;" no one could attack him anymore. (2) "I am...thy exceeding great reward"; therefore, whatever Abraham lost he could find in Him. God was comforting Abraham.
Verse 2 says, "And Abram said, Lord God, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?" Abraham told the Lord that his problem was not that simple. It seemed as if he turned the question back to the Lord: "Lord, don't You know?" The Lord likes to hear us speak. On the one hand, the Lord wants us to fear Him. On the other hand, He likes to hear us speak. When God speaks, we listen. When we speak, God listens. Abraham was telling God that his problem was not one of goods, but of a son. The matter of Canaan had been settled. Now there was the problem of a son. He said, "What wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?" This man from Damascus was not begotten of him; he was not Abraham's son. Although Abraham had heard God say, "I will make of thee a great nation" and "I will make thy seed as the dust of the earth," and although the matter of Canaan was settled, he still had no son!
God is teaching us a lesson here. Does He not know everything? Did He not know Abraham's need for a son? Yes, God knows, but He likes to see us being His friends. He wants us to enter into His heart and His mind, and He wants us to speak to Him this way. Abraham entered into God's mind in this way. God had promised him a son, but He wanted Abraham to ask for it himself. Abraham was saying that if God wanted a nation, He had to give him a son, and the son had to be born of his own house, rather than from somewhere else. The nation had to be brought in through one begotten of him, not through one bought by him. The nation should belong to his sons, not to his servants. Abraham realized that none of his three hundred eighteen trained servants nor Eliezer of Damascus could solve this problem. He needed someone begotten of him. Only someone begotten of him could solve the problem. This was what he meant when he spoke with God. Abraham was indeed a friend of God! He had entered into God's heart! Without a son, the land would have been vain and the promise would have been useless to Abraham! Without a son he could have never received the blessings. This realization was a result of God's work in Abraham.
After Abraham spoke, God did not immediately answer. He allowed Abraham to go on speaking. God is a God who is very good at listening. Verse 3 says, "And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir."