There’s no questioning the fact that Abraham was God’s man. The whole creation account followed by the fall of man, the death of Abel, the call of Noah the judgment of the flood and the tower of babel is covered in just 11 
chapters. Fourteen chapters are devoted to the life of the Patriarch, Abraham. Actually the rest of the Old Testament is about him and his descendants. And Paul, in the New Testament, looked back to Abram as the greatest of all examples of how God’s people are to be justified by faith and not works.
J. M. Boice said, “No one can understand the Old Testament without understanding Abram, for in many ways the history of redemption begins with God’s call to him. The record of Abram’s life contains the Bible’s first mention of God’s righteousness (Gen. 15:6). Matthew includes Jesus’ genealogy in his Gospel in order to trace the beginnings of salvation back to Abram (Matt. 1:1). Luke includes Zechariah’s declaration that Jesus’ birth occurred in fulfillment of God’s promise to Abram…” Yes, Abraham, the father of the Jewish Nation, the father of the Islamic nations, and the father of all Christians is the central human figure in the Bible.
Boice goes on, “Great sections of the New Testament explain the significance of Abram. To support the doctrine of justification by grace through faith, an entire chapter of Romans refers to God’s dealing with Abram. Two chapters of Galatians refer to Abram’s life to prove that salvation is given apart from good works. One of the longest paragraphs in Hebrews 11 is devoted to the growth of faith in the life of this Hebrew patriarch.” Further, Abraham is referred to as “God’s friend” twice in the Old Testament (2 Chronicles 20:7, Isaiah 41:8) and once in the New Testament (James 2:23). What was it that made Abraham God’s man? Was it his good works? Was it his obedience? Wasn’t it simply because he believed God? If Job speaks to us of hope beyond the grave and if Hosea speaks to us of divine love in-spite of our spiritual adulteries, Abraham’s life teaches us that it’s only by faith that we can have intimacy with God. As the writer of Hebrews says, “without faith it is impossible to please God” (Hebrews 11:6).