Treasury of Scripture Knowledge
Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
But they are justified freely by his grace through the redemption that is in Christ Jesus.
Therefore, since we have been declared righteous by faith, we have peace with God through our Lord Jesus Christ,
so then, understand that those who believe are the sons of Abraham.
even though we were dead in transgressions, made us alive together with Christ -- by grace you are saved! --
And so, since we have been justified by his grace, we become heirs with the confident expectation of eternal life."
Now when God made his promise to Abraham, since he could swear by no one greater, he swore by himself,
2 Peter 1:10
Therefore, brothers and sisters, make every effort to be sure of your calling and election. For by doing this you will never stumble into sin.
And he received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised, so that he would become the father of all those who believe but have never been circumcised, that they too could have righteousness credited to them.
This means it is not the children of the flesh who are the children of God; rather, the children of promise are counted as descendants.
Look at Abraham, your father, and Sarah, who gave you birth. When I summoned him, he was a lone individual, but I blessed him and gave him numerous descendants.
And I will make your descendants like the dust of the earth, so that if anyone is able to count the dust of the earth, then your descendants also can be counted.
He said to him, "What is written in the law? How do you understand it?"
So then those who believe are blessed along with Abraham the believer.
But you, brothers and sisters, are children of the promise like Isaac.