because
Luke 3:8
Bring forth therefore fruits worthy of repentance, and begin not to say within yourselves, We have Abraham to our father: for I say unto you, That God is able of these stones to raise up children unto Abraham.
Luke 16:24
And he cried and said, Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame.
Luke 16:25
But Abraham said, Son, remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented.
Luke 16:30
And he said, Nay, father Abraham: but if one went unto them from the dead, they will repent.
John 8:37-39
37
I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you.
38
I speak that which I have seen with my Father: and ye do that which ye have seen with your father.
39
They answered and said unto him, Abraham is our father. Jesus saith unto them, If ye were Abraham's children, ye would do the works of Abraham.
Philippians 3:3
For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh.
In Isaac
Genesis 21:12
And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.
Hebrews 11:18
Of whom it was said, That in Isaac shall thy seed be called: