A hinge of the whole story
The Call of Abraham
After the flood the nations scatter and grow proud at Babel, and then God does something new: He chooses one man. The call of Abraham begins the promise line that will run through the whole Old Testament and arrive at Christ, the moment God commits to bless all the families of the earth through one family.
“Now the LORD had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father’s house, unto a land that I will shew thee:”Genesis 12:1
What happened
What happened. To Abram, a man of Ur with no children and no claim on God, the LORD spoke: "Get thee out of thy country, and from thy kindred, and from thy father's house, unto a land that I will shew thee: and I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing: and I will bless them that bless thee, and curse him that curseth thee: and in thee shall all families of the earth be blessed" (Gen 12:1-3). Abram went, "not knowing whither he went" (Heb 11:8). Though he and Sarah were old and childless, God renewed the promise under the night sky: "Look now toward heaven, and tell the stars... so shall thy seed be. And he believed in the LORD; and he counted it to him for righteousness" (Gen 15:5-6). God cut a covenant with him, later sealing it with circumcision and the promise, "I will be their God" (Gen 17:8). In old age Isaac was born, the child of promise, and the line began.
Why the whole story turns here
Why the whole story turns here. From here to the end of the Old Testament, the Bible narrows to one family and one promise. After the fall and the flood revealed a world under a curse, and Babel showed the nations scattered and proud, the call of Abraham is God's answer: He will bless the whole cursed world, but He will begin with one man and one line. The threefold promise, a people, a land, and blessing for all nations, becomes the trellis on which the rest of the story grows. Israel exists because of this call; the exodus is God remembering "his covenant with Abraham" (Exod 2:24); the land, the kingdom, the temple, and the prophets' hope all flow from these verses. And the aim was never one nation only. The promise reached outward from the start, "in thee shall all families of the earth be blessed," so that the gathering of every people that ends the Bible was written into its beginning. Above all, the promise came by faith, credited to Abraham as righteousness before any law was given, setting the pattern for how sinners are made right with God in every age.
How it points to Christ
How it points to Christ. Paul says the gospel itself was preached in advance to Abraham in the words "in thee shall all nations be blessed" (Gal 3:8). The promised "seed" is fulfilled supremely in one descendant: "He saith not, And to seeds, as of many; but as of one... which is Christ" (Gal 3:16). Jesus is the true offspring of Abraham through whom the blessing at last reaches all families of the earth, so that "they which are of faith, the same are the children of Abraham" (Gal 3:7). Abraham was justified not by works but by believing God, and this becomes the pattern of salvation in Christ: "it was imputed to him for righteousness" (Rom 4:22), and it is imputed to all who trust in the One who died and rose. Jesus even said, "Abraham rejoiced to see my day: and he saw it, and was glad" (John 8:56). The whole promise line was always leading to Him.
Questions people ask
Why would God choose just one man to bless the whole world?
The choosing was never for Abraham's sake alone. From the first words the aim was global: "in thee shall all families of the earth be blessed" (Gen 12:3). God begins with one so that through his line, and finally through Christ, blessing might reach everyone.
How is Abraham connected to Jesus?
The New Testament calls Jesus the promised "seed" of Abraham through whom the blessing comes to all nations (Gal 3:16). Abraham was counted righteous by faith (Gen 15:6), and that same faith in God's promise, now fulfilled in Christ, is how sinners are justified today.