These Galatians were pagans, worshipping their different Greek and Roman pagan gods, when Paul entered their city, preached the gospel message of salvation to them, and they got saved. They turned from their sin and they believed that Jesus was the Son of God who became a man, that he lived a perfect death and he died a sacrificial death, so they could be forgiven and get into God’s heaven. They were born again, they put their trust in Jesus, they are brand new Christians filled with the Holy Spirit, the Spirit of God is working in their lives, so He’s changing them. It’s awesome.
But what was not so awesome is when these pseudo Jewish Christians show up on the scene, trying to convince the Galatians that to get saved that they need to add their own work to God’s work, the work of obeying all the Jewish laws and customs. It’s all supposed to begin with the Galatian men submitting themselves to the Jewish tradition of circumcision.