Gen 15: God's promise of an heir and many descendants to Abram. "Abram believed the Lord, and he credited it to him as righteousness"

The previous chapter mentions Melchizedek, a Canaanite who not only shared belief and worship in the same God as the Semitic Abram but who pronounced a blessing on the patriarch whom God had already blessed. This is similar to Jethro in Ex 18, a Gentile Midianite who worshipped the same God Moses did. God in the Old Testament was also calling out a people for His own from among the Gentiles. Melchizedek is set apart from anyone in the Bible, and allows him to function as a symbol of eternity. His unique priesthood foreshadows the eternal and universal priesthood of Christ, explaining also how the Messiah could come from the promise line of Abram (through the tribe of Judah) and be a priest as well as a prophet and king. Jesus could not have come from two tribes (Judah -> king, Levi -> priest), and hence became a priest not on the basis of his ancestry but on the basis of the power of an indestructible life (Heb 7:16). In this chapter, God came to Abram in a vision with a promise of many descendants and the land of Canaan as his estate.

• v1: God made this treaty with Abram after his courageous and generous act that was motivated neither for power, fame nor reward. He showed favour to people, and hence found favour with God. God spoke directly to Abram and in a timely fashion told Abram not to fear, lest the four kings should rally again. And so God told him, and us, to "not be afraid...[for] I am your shield, your very great reward", assuring us of our safety and happiness. God Himself is a shield to His people to secure them from evils, and not only will we find comfort, we will find great joy. Abram had generously refused the rewards offerred by the king of Sodom; here God comes and says that He is not only the rewarder but the reward.
• v2-3: "I pour out my complaint before him; before him I tell my trouble" (Ps 142:2). Abram's repeated complaint to God, and not of God, his opening of his burdened spirit to a faithful and compassionate God. At that point, God had already told him that He would make him a great nation (Gen 12:2), and his seed as the dust of the earth (Gen 13:6), but He had not mentioned whether his seed should be begotten or adopted. Hence with one eye on the great blessing, Abram felt that everything else was nothing to him if he could not have a child and see the great promise come to pass.
• v4-5: God addressed and answered his prayers and concerns. Abram asked for a child, but God promised that his descendants would be numerous like the stars, for God gives "exceeding abundantly above all that we ask or think" (Eph 3:20).
• v6: "Abram believed the Lord, and it was credited to him as righteousness". No one explains this verse as well as Paul, who says: "Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, "So shall your offspring be." Without weakening in his faith, he faced the fact that his body was as good as dead—since he was about a hundred years old—and that Sarah's womb was also dead. Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised. This is why "it was credited to him as righteousness." The words "it was credited to him" were written not for him alone, but also for us, to whom God will credit righteousness—for us who believe in him who raised Jesus our Lord from the dead. He was delivered over to death for our sins and was raised to life for our justification" (Rom 4:18-25) Paul quotes this verse twice (Rom 4:3, Gal 3:6) to stress how Abram believed in God, received and embraced divine revelation, and hence upon this score he was accepted by God: it is faith in God's grace that makes us righteous, without the works of the law.
• v7: God, the Lord Jehovah, brought Abram out of Ur of the Chaldees, for a higher purpose - to give him a land to possess as an inheritance.
• v8: Abram desired a sign, not because of distrust in God's power (he'd just been credited for his faith in the previous verses! =p), but he desired a sign to enable him to face an hour of temptation, when his faith might be tested. Hence his cry was Lord, help me against my unbelief.
  
• v9-11: God gave Abram a sign upon a sacrifice, rather than some extraordinary sign from heaven. He required not just any sacrifice, but wanted three animals, each three years old, at their full growth and strength i.e. the best; something that would cost Abram. Even with that compliance, God did not appear immediately (until fowls came down upon the carcasses), and the ever watchful Abram drove them away. How closely do we watch our spiritual sacrifices, that nothing comes down upon them to render them unfit for God's acceptance?
• v12-16: The prophecy came in a "thick and dreadful darkness", to strike an awe upon Abram's spirit, and foreshadow the prophecy itself. They must first be in the darkness of Egyptian slavery, then enter with joy into the promised land.
• v15: God told Abram that he should not live to see the land in the possession of his family, but on the positive side, he would also not live to see the troubles that would come upon his seed. "The righteous perish, and no one ponders it in his heart; devout men are taken away, and no one understands that the righteous are taken away to be spared from evil." (Isa 57:1)
• v17: The sign Abram yearned for was given at last when it was dark
  - smoking furnace: affliction of Abram's seed in Egypt. They were labouring in the fire, the iron furnace (Deu 4:20), to be "tested...in the furnace of affliction" (Isa 48:10), smoke and darkness around them so that they could not see the end of their troubles.
  - blazing torch: comfort in affliction, "salvation like a blazing torch" (Isa 62:1)
  - the passing of the furnace and torch between the pieces consumed and completed the sacrifice and was the confirmation of God's convenant.
• v18-21: God specified the boundaries of the land intended to be granted.