Most of us are familiar with this song:
Father Abraham had many sons
Many sons had Father Abraham
I am one of them and so are you
So let's all praise the Lord.
Yet this song is not as simple as it may sound. The Bible speaks of more than one kind of seed of Abraham.
Natural Seed (Physical Descendants):
"But you, Israel, are My servant, Jacob whom I have chosen, The descendants of Abraham My friend." Isaiah 41:8
"Now to Abraham and his Seed were the promises made. He does not say, 'And to seeds,' as of many but as of one, 'And to your Seed,' who is Christ." Galatians 3:16
Christians (Spiritual Seed):
"And if you are Christ's then you are Abraham's seed, and heirs according to the promise." Galations 3:29
Make no mistake in these verses, the Church does not equal Israel. The connection is based upon justification by faith. Look at Romans 4:3-11. Abraham was justified before he was a Gentile or Jew and before Israel became a nation. Faith alone leads to justification.