In both Acts and Galatians it is clear that there are some Gentiles who want to keep the Jewish Law. There were some Gentiles like Cornelius who worshiped and served the God of Israel and kept some forms of Jewish practice. Practices like Sabbath and food taboos were in some ways easy to adopt (especially in one was a retired soldier or independently wealthy). While circumcision was almost universally mocked by the Roman world, there were still some Gentiles who submitted to the ritual in order to fully convert to Judaism.
There might be several motivations for Gentiles who want to adopt Jewish Law. First, to accept Jesus as Savior is to reject pagan gods. By rejecting pagan gods, the Gentile converts severed many social ties and joined a religious movement unlike the rest of the ancient world. If a Gentile was fellowshiping in a Jewish Christian community, it is possible that they looked at the church as a new family. Recall that Jesus did say that those who “do his will” are his family members. Jewish law and traditions were very family orientated and provided a kind of “new family” for people who might have been rejected by their own families and friends.
Second, as Ben Witherington suggests, by accepting Jesus as messiah and Savior, they have also turned their backs on the traditional gods of the Greco-Roman world. This would include any ritual observances associated with those gods. There are virtually no rituals in the Christian church other than an initiation ritual and a shared meal. There are no sacrifices or liturgy to follow, no festivals, feast days, temple or central gathering places. The Jewish Law, in Witherington’s view, provided an opportunity for Gentile believers to concretely express their Christian identity (Galatians, 362).
Third, new religions were suspicious in the Roman world. A convert to Christianity might have a hard time explaining that they have joined a new religion that was less than 50 years old! Most of the mystery cults that were popular in the Roman world tried to connect their rituals back to ancient legends or even Egyptian gods. Since Judaism was an ancient religion, Gentile converts could avoid the charge that they were accepting a new religion, a “superstition” which was suspect in the Roman world.
The real problem for some Gentile converts to Christianity is that there is nothing about being a Christian that is externally obvious. One could identify a Jewish person as a Jew with a glance, but Christians had no distinctive dress or behavior that sets them apart as Christians. Christians were distinct in that they honor Jesus as God and Savior and (at least in theory) do good to all people. If a Christian gives alms to the poor, they are even forbidden to take credit for that act of mercy! The question of how one defines their new faith in Jesus as savior for these new Pauline churches is going to be very difficult.
This is one of the most important applications of the letter to the Galatians in a modern church setting. Very few people would argue that Christians ought to be keeping the whole law (although there are a few). More likely is the claim that one must do a series of rituals in order to be right with God, or that one must subscribe to a particular doctrinal formulation, or that one must avoid certain lifestyles or behaviors. Paul never says that one must act like a Christian in order to be right with God – one is right with God because they have been adopted into God’s family and they are his children.
Paul is not talking about a religion in Galatians, but rather a relationship with God.