Further Thought: “In almost every church there were some members who were Jews by birth. To these converts the Jewish teachers found ready access, and through them gained a foot-hold in the churches. It was impossible, by scriptural arguments, to overthrow the doctrines taught by Paul; Image © Stan Myers from GoodSalt.com hence they resorted to the most unscrupulous measures to counteract his influence and weaken his authority. They declared that he had not been a disciple of Jesus, and had received no commission from [H]im; yet he had presumed to teach doctrines directly opposed to those held by Peter, James, and the other apostles.
Read more at the source: Friday: Further Thought – Paul’s Authority and Gospel