Hebrews 11:12 - Therefore from on man, and him as good as dead, were born as many as the stars of the sky in the multitude - innumerable as the sand which is by the seashore.
In the book of Genesis, God gave Abraham three word pictures of his children. If you understand what the pictures mean, you will understand that the church and Israel can never replace each other.
First, God says that Abraham's seed shall be as the dust of the earth. "And I will make your descendants as the dust of the earth; so that if a man could number the dust of the earth, then your descendants also could be numbered" (Genesis 13:16). He's speaking of Abraham's physical descendants only, regardless of faith, including the Jews and the Arabs from Ishmael.
Second, God speaks of the sand of the sea. " Multiplying I will multiply your descendants as the stars o the heaven and the sand which is on the seashore" (Genesis 22:17). The "sand which is on the seashore" is through Isaac, representing the nation of Israel.
Also in Genesis 22:17, God speaks of the stars of the heavens, referring to the Gentiles through the church. Just as a star produces light, Jesus said to believers, "You are the light of the world" (Matthew 5:14).
Source: Life Lessons to Live By - Abraham's Seed in Scripture