The Jerusalem that is above is free, and she is our mother.
Hagar’s son, Ishmael, was the result of a human attempt to fulfill God’s promise (see Genesis 16). When Sarah became pregnant and bore a son, Isaac, she decided that Hagar and Ishmael became a liability (Gen. 21:1–21). When Ishmael mocked Isaac, Sarah ordered them to leave. With sadness, Abraham sent them out into the desert, trusting God to care for them. He knew that it was Isaac and not Ishmael who was the son of promise.
In Galatians, Paul read this story as a parable of the gospel, an analogy of the doctrinal narrative he had presented. It reflected the truths about promise, law, and Christ that he been describing. Furthermore, this method of interpreting the Torah was a common rabbinic strategy in his day. By using it, Paul was beating the Judaizers at their own game.
This parable or analogy depended upon the contrast between the two lines of Abraham (vv. 21–23). On the one hand, Hagar was a slave. Her son Ishmael was born by normal human means. On the other hand, Sarah was free. Her son Isaac was born miraculously as a result of God’s promise. Clearly, Sarah and Isaac were the superior line.
Paul interpreted this figuratively as a contrast between the true gospel and legalism (vv. 24–27). Hagar and Ishmael represent the covenant given at Mount Sinai, that is, the Mosaic Law or the earthly Jerusalem. Its children are slaves. Sarah and Isaac represent the promise given to Abraham and its fulfillment in Christ and the gospel, or the heavenly Jerusalem. Its children are free. One side shows that human capabilities were insufficient. The other rests on a foundation of our faith and God’s faithfulness. This is a reason for great joy, as when a barren woman becomes able to bear children.
Apply the Word
Verse 27 quotes Isaiah 54:1. In its original context, this verse is about the return of Jewish exiles to Jerusalem. In Paul’s analogy, it’s also a picture of the nations coming to Christ through the gospel. Revelation 21 includes this powerful description of the new Jerusalem: “God’s dwelling place is now among the people, and he will dwell with them.”