The epistles were Holy Spirit inspired and can be relied on. Most of the misunderstanding is about the transition from the Old to the New Covenant - it didn’t happen until He died and rose again. His words are always compliant with the Old Covenant and many mistake them as New Covenant provisions.
Not Catholic teaching, but that of the dispensationalist sect of Protestantism. The Council of Trent condemned the idea that Jesus is not a lawgiver whom Christians must hear and obey.