The men of the Bible were just that; men. The people of the Bible were not any holier than we are today. Each made good and bad decisions. God allows us to see their decisions (the good, bad, and the indifferent ones) in the Bible to show us that those whom He calls holy and blessed were just as flailed as we are today; but He chose them anyway just as He chooses us today. Hebrews 11 shows us people whom God has called faithful. Hebrews shows the end result to encourage us in our daily walks. The book of Genesis shows us the process by which each went through to go from pagan to holy and all the good and bad in each person. Moses writes the book to show where the nation of Israel generated from. He assures us by the examples of Abraham, Isaac, Jacob and the rest of the patriarchs, that God’s mercies never fail those whom He chooses to be His people, and to profess his Name in earth, but in all their afflictions and persecutions He assists them, sends comfort, and delivers them, so that the beginning, increase, preservation and success of it might be attributed to God only.1
In Genesis 21, Isaac was born fulfilling the promise God made to Abraham and Sarah. Isaac was the fulfillment of the covenant God made with Abraham in Genesis 12. In the Abrahamic Covenant, God promises to increase Abraham’s seed (descendants), to give him the land of Canaan, and to bless him.2 It is through Isaac that God will fulfill God’ promise to increase Abraham’s seed (Genesis 17:21 “But My covenant I will establish with Isaac, whom Sarah will bear to you at this season next year.”). God chose Isaac to bring about the nation of Israel.
Hebrews 11:20 says, “By faith Isaac invoked future blessings on Jacob and Esau.” In comparison to his father and his son Jacob, Isaac is mentioned less in Genesis. I see him as the in between person who God used to fulfill His promise to Abraham. The Book of Genesis does show us his birth in Genesis 21; Abraham commanded to sacrifice him in Genesis 22; his marriage to Rebekah in Genesis 25; the birth of Jacob and Esau in Genesis 25; his failing to be truthful (like his father) in Genesis 26; and him being deceived by Rebekah and Jacob in Genesis 27. In the end, Isaac fulfilled his purpose to bring about Jacob who the twelve tribes of Israel come. It is through Jacob the Messiah comes and Jesus Christ is the ultimate fulfillment of the Abrahamic Covenant.
1 “The 1599 Geneva Study Bible,”biblestudytools.org, N.A. http://www.biblestudytools.com/commentaries/geneva-study-bible/
2 Keith H. Essex, The Abrahamic Covenant. (The Master’s Seminary Journal: Sun Valley, CA, 1999), 191.