Expositor's Bible Commentary Commentary Galatians 4:30

"Howbeit what saith the scripture? Cast out the handmaid and her son: for the son of the handmaid shall not inherit with the son of the freewoman." — Galatians 4:30 (ASV)

Second, the Christians at Galatia must recognize the incompatibility of manmade and God-made religion and respond by casting out the legalizers. Those born after the flesh (v.29) will never share in the inheritance God has reserved for his true children, born after the Spirit. Therefore, Christians must reject both legalism and those who teach it. Taking a story from Genesis that the Jews undoubtedly interpreted as a statement of God’s rejection of the Gentiles and applying it instead to the exclusion of unbelieving Jews from Christianity probably infuriated Paul’s opponents, but his point was well taken. God does not look on physical descent but on spiritual affinity. The true sons of Abraham are those who are born of the Spirit.