The Freedom of the Promise: Unpacking the Allegory of the Two Covenants

The persistent temptation of the human heart is to try to perfect through self-effort what God began through grace. In the early church, the churches of Galatia faced an urgent theological threat: false teachers known as Judaizers were subtly shifting the basis of acceptance with God. They did not dismiss Jesus entirely; instead, they insisted that faith in Him was merely a baseline to which believers had to add legal performance, specifically the keeping of the Mosaic law and circumcision.

In Galatians 4:21–31, the Apostle Paul addresses this performance-based mindset directly. He challenges those who desire to live under the law to truly listen to what the law says, using a historical allegory from the Torah itself—the accounts of Sarah, Hagar, Isaac, and Ishmael—to show that grace and human merit can never coexist.

The Error of Assisting God: Flesh vs. Promise

To understand the power of Paul’s argument, we must return to Genesis 16 and 21. God explicitly promised Abraham a son and a global inheritance through his wife, Sarah. However, Sarah was barren, and as years passed without a child, impatience clouded their faith. Operating on human strategy rather than divine revelation, Sarah persuaded Abraham to take her Egyptian slave, Hagar, to produce an heir.

The resulting birth of Ishmael was a birth accomplished kata sarka—according to the flesh. It was the product of human planning, physical capability, and worldly wisdom trying to force a divine promise.

Years later, when Abraham was nearly one hundred years old and Sarah was ninety, God intervened supernaturally. Operating completely independent of human strength, God opened Sarah’s womb to bring about Isaac, the child of promise. This birth was accomplished kata pneuma—according to the Spirit.

The Allegory of Two Cities

Paul takes these historical realities and demonstrates their deeper prophetic meaning, showing that these two women represent two distinct systems:

• Hagar and Mount Sinai: Hagar corresponds to the covenant established at Mount Sinai. This system relies on human performance to achieve righteousness. Paul explicitly links this to the contemporary, earthly Jerusalem of his day, which was trapped in a legalistic system of bondage. Its children are spiritual slaves, continually striving for an acceptance they can never earn.
• Sarah and the Jerusalem Above: Sarah corresponds to the heavenly Jerusalem. This is the community of faith, existing in perfect freedom. She is the mother of all who rest in the finished work of Jesus Christ. This system relies entirely on God’s supernatural, sovereign grace.

To confirm this, Paul references Isaiah 54:1, showing that the family of grace—born supernaturally out of desolation and barrenness—will vastly outnumber the family of human effort, expanding to include believers from every nation across the globe.

The Command to Cast Out Legalism

The ancient history also mirrors an ongoing spiritual conflict. In Genesis 21, during the celebration of Isaac’s growth, Ishmael was caught mocking and persecuting the child of promise. Paul notes that this hostility remains unchanged: those born according to the flesh will always oppose those born according to the Spirit. Legalism always seeks to manipulate and control grace.

The scriptural remedy is absolute: “Cast out the bondwoman and her son, for the son of the bondwoman shall not be an heir with the son of the free woman.”

The Greek word used here (ekbale) is an intense command to eject something decisively. Paul leaves no room for compromise or a middle ground. You cannot mix a system of human effort with a system of divine grace. They are fundamentally incompatible. If salvation or your standing before God depends even partially on your performance, it ceases to be grace.

Living From Salvation, Not For Salvation

This exposition brings us to a foundational truth for the Christian life: We do not live righteously so that we may be saved; we live righteously because we are saved.

Legalism reverses this order, turning good works into a mechanism to maintain God’s favor. True obedience is not the root of salvation, but its fruit. The ability to walk in genuine holiness comes not from self-effort, but from the indwelling Holy Spirit, who changes our desires and empowers us to live a life that pleases God out of deep gratitude for an inheritance already secured.