What is the difference between what Paul defends in Corinthians and what he defends in Galatians?

Les explains that in I and II Corinthians Paul was dealing with problems in the congregation and a constant attack on his person. People were decrying him as an imposter and a fake, saying he had drummed up something on his own and did not have the authority of Peter, James and John. So in those letters, Les teaches, Paul is always defending his apostleship. In Galatians, however, the average reader may not discern the difference, but Les points out that Paul is not so much defending his person as he is his doctrine. Doctrine, or teaching, is primary; without it you have nothing, and experience alone does not set your feet in concrete. In Galatians Paul is refuting false doctrine and false teaching that had crept into the Galatian churches and every church he founded. Les notes that this false teaching of legalism has plagued Christianity through the centuries and is still relevant, coming in many subtle shapes and forms, not just temple worship and Judaism.