Children of Abraham

“Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham’s offspring – not only to those who are of the law but also to those who are of the faith of Abraham. He is the father of us all.” Romans 4:16
When I was in Sunday school one of the more popular songs we sang was ‘Father Abraham had many sons, Many sons had father Abraham, I am one of them and so are you, So let’s just praise the Lord’. When I got a bit older I wondered about it. Abraham was the father of Isaac, Isaac the father of Jacob, and Jacob the father of the twelve tribes of Israel. I’m not Jewish*, so how could I be one of the many sons (children) of Abraham?
Paul explains to us here what it means to be a child of Abraham. Abraham has two types of children: those after the flesh (‘of the law’, i.e. the physical descendants of Abraham, to whom the Law was given by God through Moses), and those of faith.
What did Abraham have faith in? He had faith in God’s promise to him, that through his descendants the Messiah would come to save the world from sin. Although at that time Abraham was old and had no children, he believed God that it would happen. And we are told, “Abram believed the Lord, and He credited it to him as righteousness” (Gen. 15:6).
If we have faith in Jesus as Messiah, then we are exercising the same faith that Abraham had. This makes us Abraham’s spiritual children.

*My great-grandmother was Jewish, but despite much effort by other family members researching our family tree, we know very little else about her.