Allegories are not very convincing, but like pictures they visualize a matter. If Paul had not brought in advance indisputable arguments for the righteousness of faith over against the righteousness of works this allegory would do little good. Having first fortified his case with invincible arguments, he can afford to inject this allegory to add impressiveness and beauty to his presentation.
VERSES 24, 25. For these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar. For this Agar is mount Sinai in Arabia.
In this allegory Abraham represents God. Abraham had two sons, born respectively of Hagar and Sarah. The two women represent the two Testaments. The Old Testament is Mount Sinai, the bondwoman, Hagar. The Arabians call Mount Sinai Agar. It may be that the similarity of these two names gave Paul his idea for this allegory. As Hagar bore Abraham a son who was not an heir but a servant, so Sinai, the Law, the allegorical Hagar, bore God a carnal and servile people of the Law without promise. The Law has a promise but it is a conditional promise, depending upon whether people fulfill the Law.
The Jews regarded the conditional promises of the Law as if they were unconditional. When the prophets foretold the destruction of Jerusalem, the Jews stoned them as blasphemers of God. They never gave it any thought that there was a condition attached to the Law which reads: "If you keep the commandments it shall be well with thee."
VERSE 25. And answereth to Jerusalem which now is, and is in bondage with her children.
A little while ago Paul called Mount Sinai, Hagar. He would now gladly make Jerusalem the Sarah of the New Testament, but he cannot. The earthly Jerusalem is not Sarah, but a part of Hagar. Hagar lives there in the home of the Law, the Temple, the priesthood, the ceremonies, and whatever else was ordained in the Law at Mount Sinai.
I would have been tempted to call Jerusalem, Sarah, or the New Testament. I would have been pleased with this turn of the allegory. It goes to show that not everybody has the gift of allegory. Would you not think it perfectly proper to call Sinai Hagar and Jerusalem Sarah? True, Paul does call Sarah Jerusalem. But he has the spiritual and heavenly Jerusalem in mind, not the earthly Jerusalem. Sarah represents that spiritual Jerusalem where there is no Law but only the promise, and where the inhabitants are free.
To show that the Law has been quite abolished, the earthly Jerusalem was completely destroyed with all her ornaments, temples, and ceremonies.
VERSE 26. But Jerusalem which is above is free, which is the mother of us all.
The earthly Jerusalem with its ordinances and laws represents Hagar and her offspring. They are slaves to the Law, sin and death. But the heavenly Jerusalem is Sarah, the free woman. This heavenly Jerusalem is the Church, that is to say the number of all believers throughout the world, having one and the same Gospel, one and the same faith in Christ, one and the same Holy Ghost, and the same sacraments.