In the letter to the Galatians, the old belief which is having a hard time dying was the necessity for a person to become first a Jew, men by circumcision, women by baptism, before then becoming Christians.

It was essentially placing oneself under the Old Testament Law, and then, somehow, fitting in Jesus and his sacrifice for our sins. It was trying to have both of these religious beliefs somehow live together.

The problem is, they cannot.