Even though Paul had to withstand Peter, he nevertheless acknowledged that he and Peter were both Jews, and that they both agreed on the great doctrine of justification by grace through faith and not by the works of the law. Peter's temporary compromise in conduct was not because of doctrinal differences with Paul.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8