The end of Genesis 11 introduces a man whom James Montgomery Boice considers “apart from Jesus Christ . . . is probably the most important person in the Bible.” First introduced as Abram, God renames him Abraham. Boice continues:
Abraham is a giant in Scripture—his stature is far greater than that of Moses, David, or Paul. These latter three were great men, and God used them in great ways, even giving portions of the Scriptures to us through them. But each of them would have agreed without qualification that Abraham was his father in faith.
Boice makes a solid case in stating this opinion. Yet, one must note that Abraham’s stature is not merely confined to the Old Testament, but also influenced two other religions besides Judaism: Christianity and Islam.
We first meet Abram in Genesis 11:
27Now these are the generations of Terah: Terah begat Abram, Nahor, and Haran; and Haran begat Lot. 28And Haran died before his father Terah in the land of his nativity, in Ur of the Chaldees. 29And Abram and Nahor took them wives: the name of Abram’s wife was Sarai; and the name of Nahor’s wife, Milcah, the daughter of Haran, the father of Milcah, and the father of Iscah. 30But Sarai was barren; she had no child.
31And Terah took Abram his son, and Lot the son of Haran his son’s son, and Sarai his daughter in law, his son Abram’s wife; and they went forth with them from Ur of the Chaldees, to go into the land of Canaan; and they came unto Haran, and dwelt there. 32And the days of Terah were two hundred and five years: and Terah died in Haran.
This genealogy is given immediately after the account of the Tower of Babel, and serves as a listing of Shem’s descendants. Who is Shem? Shem is one of the three sons of Noah (along with Ham and Japheth). Shem and his brother Japheth respected their father while he lay exposed after a time of drunkenness and thus was blessed by Noah (see Genesis 9:18-27). Whereas Ham and his descendants migrated southward toward Northern Africa and Japheth migrated north, Shem’s descendants travelled east and settled in the easternmost part of the Fertile Crescent.
Among the descendants of Shem, God focused on a family of Terah who lived in Ur of the Chaldeans. This family and this culture were pagan, as archaeologists have uncovered. As stated in verse 31, Terah intended to proceed to Canaan, but settled short of there in Haran. Abraham would proceed, but not based upon his earthly father’s leading, but on his Heavenly Father’s will. Instead of Canaan being their place of choice, Canaan ended up being God’s place of promise not simply for Abraham’s immediate family, but for his descendants. With this, he would go from Abram (which means ‘exalted father’) to Abraham (which means ‘father of a multitude’). This incident would not be the first time that God would intervene with his promise over and against their plans.
This chapter gives a brief but (hopefully) helpful overview of the Religions of Abraham: Judaism, Christianity, and to a lesser extent Islam in their origins.
Abraham’s Influence in Judaism
While Abraham may not have recognized that he would be the founder of Christianity nor Islam, he did understand that he would be the father of a people.
1Now 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: 2And I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing: 3And I will bless them that bless thee, and curse him that curseth thee: and in thee shall all families of the earth be blessed (Genesis 12:1-3).
That nation which would come from Abraham would be known as God’s chosen people, whose history the entire Bible outlines. The beginnings of this reality were rather rocky. Sojourns into Egypt when Sarah was taken into Abimelech’s harem (Genesis 12:10-20), a rescue operation to retrieve his nephew Lot from wartime captivity (Genesis 14:1-16), and the loophole Sarah devised to bring this promised offspring into the world through her handmaiden Hagar (Genesis 16) would all have significant consequences in later events which would be detrimental to the Jewish nation.
This nation would be from the son of promise known as the Hebrew nation, the Jews. And all through these obstacles, God continued by His sovereign grace to reinstill his promised covenant to Abraham. For instance, examine Genesis 15:1-6:
1After 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. 2And Abram said, LORD God, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus? 3And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir. 4And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir. 5And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. 6And he believed in the LORD; and he counted it to him for righteousness. (Genesis 15:1-6).
Abraham began to wonder whether God would fulfill the promise He made to him back in Genesis 12. When God made this promise to Abraham, he was 75 years old! His wife was barren—she could not have children. Abraham asked Yahweh, “O LORD God, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus? . . . Behold, you have given me no offspring” (Genesis 15:2-3a).” The response? “This man shall not be your heir; your very own son shall be your heir. . . . Look toward the heaven, and number the stars, if you are able to number them. . . . So shall your offspring be” (15:4-5). Abraham believed God—to which God credited this to his account (15:6)—a verse that will figure prominently in New Testament writings as foundational to Christianity, and show that God intended the faith of the Hebrew people to be based on faith which was motivated by the Law He gave through Moses.
When Abram tried to circumvent this with a plan his wife devised by going into Hagar, from whom Ishmael came, God reiterated his covenant with Abram but also made it clear through whom this child would be born: “I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of people shall come from her” (Genesis 17:16, emphases added). Here, God clearly showed that the child of promise would come through Abraham and Sarah. Given their advancing ages, they needed this continual reassurance that God had not forgotten His promise nor forsaken His servants.
Fast forward ahead to Genesis 21, God fulfills His promise to the 99-year-old Abraham and the 90-year-old Sarah. Sarah would conceive and bear a son of promise and would name him ‘laughter’ (which is the Hebrew translation for the name ‘Isaac’). Why ‘laughter’? How would you respond if an angel approached you at 90 years old and told you that you would father or bear a son in the natural way—conception, nine-month gestation period, and natural childbirth? You may laugh at the absurdity of the notion. So did Abraham (Genesis 17:17), as did Sarah (18:12). Yet, nothing is too hard for the Lord (18:14). Once Isaac was born, Sarah noted, “God hath made me to laugh, so that all that hear will laugh with me” (21:6).
Russell Moore shows how this promise and its fulfillment would be foundational to the Jewish people (and to Christians as well) in the generations to come:
With the foundation of the Abrahamic promise, God further reveals the contours of biblical hope. Through the Mosaic covenant he outlines the blessings of an obedient nation and the curses of a disobedient people. In the Davidic covenant he promises a son to David who will build a dwelling place for God, defeat God’s enemies, and rule the people in the wisdom of the Spirit (2 Sam. 7; Pss. 2; 73; 89). In the prophesied new covenant God promises to unite fractured nations of Israel and Judah into one people, a people who all know Yahweh, are forgiven of their sins, and are restored as a nation in the promised land (Jer. 31:31-40). 
As we transition into Abraham’s influence on Christianity, let us look to the book of Hebrews, chapter 6, verses 13 through 18:
13For when God made promise to Abraham, because he could swear by no greater, he sware by himself, 14Saying, Surely blessing I will bless thee, and multiplying I will multiply thee. 15And so, after he had patiently endured, he obtained the promise. 16For men verily swear by the greater: and an oath for confirmation is to them an end of all strife. 17Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath: 18That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us.
James Montgomery Boice, Ordinary Men Called by God: A Study of Abraham, Moses, and David (Grand Rapids, MI: Kregel Publications, 1982), 13.
Henry Morris, The Genesis Record: A Scientific and Devotional Commentary on the Book of Beginnings (Grand Rapids: Baker Book House, 1976), 288.
Russell Moore, Personal and Cosmic Eschatology in A Theology for the Church, ed. Daniel Akin (Nashville: Broadman & Holman Academic, 2007), 861.