The book of James is aimed at telling believers to do good works to make their beliefs come alive. It's for believers, not for telling non-believers that they can be saved by works. It's often misinterpreted that way.
You don't think James the brother of Jesus might have written that to straighten out the hogwash that Paul was spewing? And then Jesus praised the church at Ephesus for expelling Paul. Then Paul bemoans his expulsion in his letter to Timothy thus verifying Jesus' message in Revelation 2.
People who knew much more than you included the letters of Paul in the Bible because they knew them to be true.
Peter recognized the validity of Paul's teachings and their harmony with those of Christ.
