Another enriching post by Mike Ratliff:
The root of most heresies springs from those who profess Christ as Saviour, but who believe in various ways that what the Christian receives at Salvation is not sufficient. Something else must be added in order for the Christian to enter into a fuller relationship with God or to go deeper into the things of God. Some even go so far as to say that unless certain things are added to salvation then it is not complete and, therefore, void. A good example of this is found in the book of Galatians. Some Judiazers had entered the churches Paul and planted in Galatia. They were teaching that salvation was indeed by Christ, but it was not complete unless the converts also were circumcised and kept the Law of Moses.
You can read the rest here.