Romans 4:11  “…he received the sign of circumcision…yet being uncircumcised…he might be the father of all them that believe, though they be not circumcised”
Abraham became the father of many nations.  Not just the ancestor of different groups of people, but the one who showed that faith or belief in Christ is counted as righteousness.  All who put their faith in Christ for salvation are descendants of Abraham.  The true descendants.

13  “…the promise, that he should be the heir of the world was not…through the law, but through the righteousness of faith”

17  “…God, who quickeneth the dead, and calleth those things which be not as though they were”

19-20  “…being not weak in faith, he considered not his own body now dead…the deadness of Sarah’s womb…He staggered not at the promise of God…”

21  “…being fully persuaded that, what He had promised, He was able also to perform”
Even though things looked as through God’s promises would not come true, Abraham continued to have faith in Him.  That faith was counted to him as righteousness.  And God did fulfill His promises to Abraham, and continues to do so, as He is ever faithful.

I hope you enjoy reading and studying His word.  May it accomplish what He desires.  Please feel free to comment or post questions.  Thanks for reading!