One of Noah's sons was named Shem. Several generations after the flood, we come to a descendant of Shem named Terah, who lived in Ur, which was in Mesopotamia. Terah had a son named Abram whose name is later changed by God to Abraham. God also changes the name of Sarai, Abraham's wife, to Sarah (Genesis 17:5, 15). Although Sarah is unable to have children (11:30), God chooses Abraham and Sarah to be the progenitors of a nation that would be a very special and important part of His plan to deal with sin, and give His beloved creatures a way back to the tree of life. In keeping with this, God makes some special promises to Abraham. On his part, Abraham provides us with an example of faith in God, which gives us some insight as to why God chose him.
The Promises to Abraham, Genesis 12:1-7
God makes three distinct promises to Abraham: in 12:2 He promises to make him a great nation; in 12:3 He promises that all families of the earth would be blessed through him; and in 12:7 He promises to give him the land of Canaan. Let us look at these promises individually.
1) God promises to make Abraham a great nation. As a part of this promise, God will give Abraham innumerable descendants, as He states in Genesis 13:16; 15:5; 22:17; 17:5. In fact, in 17:5 God goes so far as to say that Abraham would be a father of many nations. We see this promise fulfilled later in the Old Testament, when Abraham's descendants have settled in the land of promise and grow to be, as King Solomon notes in I Kings 3:8, innumerable. But the nation of Israel is not the only nation that is descended from Abraham. The Ishmaelites (Arabs) and the Edomites (Idumeans) also came from Abraham's descendants, to name two (Genesis 25:12-16; 36:1-9). However, we actually see the full significance of this promise in the New Testament. People of all nations are brought to God the Father through Abraham's greatest descendant, Jesus Christ (Colossians 3:9-11). In Romans 4:13-18, we find that all people of all nations who have the kind of faith that Abraham had are Abraham's descendants in God's eyes, and it is in this way that the promise finds its ultimate fulfillment. So, this promise is ultimately fulfilled not in any physical nation, but spiritually, in Christ.
2) God promises Abraham the land of Canaan. He even tells him what the ultimate extent of the land would be in Genesis 15:18. We find that God gives them that land, just exactly as He had promised, in the time of Joshua (Joshua 21:43-45). The Israelites took possession of the land to its fullest extent in the time of King Solomon (I Kings 4:21). We make a mistake if we think that this promise is yet to be fulfilled to the Israelites; it was fulfilled nearly 1,000 years before Christ came. However, just as the promise of being a great nation is ultimately fulfilled in God's spiritual people in Christ, this promise also has an ultimate fulfillment in the spiritual realm. As we read through the history of the Old Testament, we find that the Israelites - like all other nations - continually turn from God and despise His law. Finally, He decides to let the land be taken from them, and for the people to be carried away into exile. However, even as He warns them through the prophets of their coming defeat, He promises ultimate redemption for those individuals who are faithful to Him or repent and return to Him. Along with these promises of ultimate redemption are promises of an anointed King - Messiah - and of a kingdom that would have no end. Although this kingdom is described using terms that would be familiar to the original hearers, nonetheless the kingdom is often described in such a way as to indicate that it was not going to be a literal, physical place (for example, Isaiah 2:1-4). We will see the ultimate, spiritual fulfillment of this promise in the New Testament, as well.
3) God promises that all families and nations of the earth would be blessed in Abraham. Whereas we can postulate various ways in which the physical nation of Israel might have been a positive influence on the nations around them, there are clearer ways that the idolatrous nations had a negative impact on Israel. For example, see Numbers 25:1-3; Judges 2:11-19; I Samuel 8:4-9; and II Kings 21:1-9. So, we do not see a clear fulfillment of this most wonderful of all three promises in the Old Testament. It is in the New Testament that this promise is fulfilled.
The Faith of Abraham, Genesis 15:1-6
Let us go back to the first promise, that Abraham would have innumerable descendants, who would make a great nation. This would be no small feat, since Abraham was already 75 years old when he moved to Canaan (12:4-5), and as we have noted, Sarah his wife was barren. Nonetheless God promises it, and Abraham believes Him. This faith God accounts for righteousness.
What does it mean, that God accounted Abraham's faith for righteousness? Well, Abraham was not a sinless man (for example, see chapter 16:1-6). As in the case of Adam and Eve, sin deserves punishment, and the penalty is death - Genesis 2:17; Romans 6:23a. Yet, because of Abraham's faith, God accounted him as righteous: in other words, He did not take Abraham's sins into account, but regarded him as though he had not sinned. This is certainly merciful on God's part. But how is it fair? How can God let this sinner go unpunished? That does not seem like justice. This problem is not solved for us in the Old Testament.
Now, what does it mean to say that Abraham believed God? Does it merely mean that he intellectually acknowledged God's existence? Does it simply mean that he felt in his heart that God is good and powerful? No, it is much more than that. When we consider that Abraham believed God's promise of children in spite of his advanced age and his wife's inability to conceive, we begin to see that Abraham had a complete, childlike trust in God.
As we read the account of Abraham's life, we find that without exception he does what God tells him to do. This is most poignant in chapter 22, when God tells him to sacrifice Isaac - the son for whom he had waited for so many years. Here we see Abraham getting up early in the morning to obey God's command, whether he understood it or not. It is here in this passage where we truly see Abraham's faith in its fullness. He completely trusts God to work things out and accomplish what He has promised, and he sets out to carry out God's instructions. Of course, God did not intend to allow Abraham to carry out the sacrifice, but was testing him - and Abraham passed. In verses 16-18 the angel clearly states that it is because Abraham has this kind of faith that God decided to lavish these very special blessings upon him.
In the life of Abraham we can see that a simple, trusting, obedient faith is the kind that pleases God. There is no place in scripture that gives any hope to people who have any other kind of faith. On the contrary, see James 2:14-26.