Matthew 21:23

And when he was come into the temple, the chief priests and the elders of the people came unto him as he was teaching, and said, By what authority does thou these things? and who gave thee this authority?

Although propounded by Jesus' enemies, this question must rank as one of the most important ever asked. This question should be addressed to all preachers and teachers of every religion; and every church should also answer it. If the authority is from man, the actions and teachings are worthless; if from God, they are valid and should be accepted. Christ answered their question by asking another which revealed that they already knew the correct answer and were, therefore, asking in the hope of finding some grounds of complaint.