The hearers are to judge what is taught

"Christ says in Matthew 7[:15], 'beware of false prophets, who come to you in sheep's clothing but inwardly are ravenous wolves.' Observing that he here assigns the judgment not to the prophets and teachers but to the pupils or to the sheep. For how could one beware of false prophets unless one examined judged, and gave a decision on their teaching? There can be no false prophets among the hearers but only among the teachers. Consequently all teachers and their teaching should and must be subject to the judgment of the hearers." - Martin Luther, Right and Power of a Christian Church, Pg. 327