Isaac was the child of promise to Abraham, even in his old age.
Guess what? You and I are children of promise in Christ Jesus:
"Now we, brethren, as Isaac was, are the children of promise." (Galatians 4: 28)
There will be challenges to our new, blessed standing in Christ:
"But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now." (Galatians 4: 29)
We will face persecution not just from the world, but men and women in the Body of Christ who trust in the flesh, who see their efforts fail, and who still seek to justify themselves through the law.
Which is why Paul warned the Galatians, who were going back to the Ten Commandments:
"But if ye bite and devour one another, take heed that ye be not consumed one of another." (Galatians 5: 15)
Now, the remedy for avoiding these divisions is found in the next verses in Galatians chapter four:
30Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.
31So then, brethren, we are not children of the bondwoman, but of the free." (Galatians 4: 30-31)
We are free from the law in Christ (Romans 7:4-7), and we now have the law of the Spirit of life living and directing us from within (Romans 8:2-3).
We are blessed with all spiritual blessings in Christ Jesus (Ephesians 1: 3) because of what He did on the Cross, the very things which Isaac blessed Jacob and Esau, concerning things to come.
Today, because of Jesus, we are blessed, because the things prophesied concerning Jesus, have all come to pass!