Abraham is the father of the faithful. He is a type of God the Father; Isaac was a type of the Son, Jesus Christ. Humanly, he is the head of the family—of those who are loved by God, who love God, and are obedient to Him.
Abraham is the patriarch. He is the leader and elder. He is the primary example among men. Considering the way God speaks about him, there has been nobody on earth as great as Abraham, except for Jesus Christ. What an example we have here!
If we are Christ's, we are Abraham's seed and no other's (Galatians 3:29). Because we are Abraham's children, we are heirs according to the promise.
In Abraham, we are looking at one of the prime examples in all of mankind. In Genesis 26:5, the promise is repeated to Isaac, and God says to him, "Because that Abraham obeyed My voice, and kept My charge, My commandments, My statutes, and My laws." That covers everything, does it not? Consider this in reference to Genesis 18. This is God speaking:
Seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him? For I know him [meaning "by experience I know him"], that he will command his children and his household after him, and they shall keep the way of the LORD, to do justice and judgment; that the LORD may bring upon Abraham that which He has spoken to him. (Genesis 18:18-19)
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Nineteen)