Commentaries:
The births of Ishmael and Isaac are recorded in Genesis 16 and 21. Though this happened long before the Ten Commandments and the other laws were given through Moses, Paul refers to this portion of Scripture as the law! Obviously, Paul uses "law" to mean the entire Pentateuch or Torah (the first five books of the Bible), not just the Commandments. In Galatians 4:24, he specifically mentions the Old and New Covenants.
Earl L. Henn
What Was the Law 'Added Because of Transgressions'?
He gives us this example and then specifically tells us that what is seemingly a simple historical narrative is actually an allegory. In other words, as important as the story is in its effect on the continuation of the promises, it also has continuous application in certain spiritual circumstances. What at first seems only to be an interesting historical reference has a dual use. Much of the Old Testament fits this usage, providing us with valuable spiritual instruction through its examples.
John W. Ritenbaugh
The Offerings of Leviticus (Part One): Introduction
Other Forerunner Commentary entries containing Galatians 4:23:
Genesis 3:15
2 Kings 4:8-37
Galatians 3:17-25
Galatians 3:19