Paul develops the theme of Law’s temporary responsibility by fleshing out the image of a guardian that looks after the young child. During childhood, it is impossible to tell the difference between children and slaves, both are restricted, both under compulsion, both unable to make decisions for themselves.
In other words, prior to the coming of the Gospel, even though the Jews had a covenant with God, it was impossible in some respects to distinguish them from the Gentiles. The Gentiles were slaves to their masters, false gods but the Jews were in practice, salves to their master, The Law. The Gospel marks coming of age, legal adoption, freedom for Jew and Gentile alike.
So, the question for Jews and Gentiles alike is “why would you go back, why would you regress?” To go back from the Gospel is to return to your previous position. For Gentile believers, adding in circumcision was regression not progress because it meant a return to the condition of slavery.
Note that there is some emotional game play going on as well. The opponents of Paul are manipulating the Galatians pretending to particularly care for them, flattering them, giving them lots of attention. So Paul reminds them of his personal, intimate connection with them. This is to get their attention and warn them that the manipulation is intended to harm them, to shut them out from the Gospel.
To drive home his point, Paul uses an allegory with a twist. He tells the story of two sons, Hagar’s son and Sarah’s son. Sarah’s son Isaac is the free born son of promise, Hagar’s is the slave’s son. He then aligns the sons with two mountains. Isaac is linked to Jerusalem, possibly because the city was linked to the mountain where Abraham took Isaac to offer him and received him back as the promise was affirmed. The twist is that Paul aligns the slave-born son with Mount Sinai and the Law. Torah, instead of marking you out as part of God’s people and an heir of the promise can only exclude you from the promise and the inheritance.
Faithroots 