What does "safe and sane" mean in this passage?

Question

Father Brown reveals his secret of capturing criminals in this passage from The Secret of Father Brown by G. K. Chesterton:

No man's really any good till he knows how bad he is, or might be; till he's realized exactly how much right he has to all this snobbery, and sneering, and talking about "criminals," as if they were apes in a forest ten thousand miles away; till he's got rid of all the dirty self-deception of talking about low types and deficient skulls; till he's squeezed out of his soul the last drop of the oil of the Pharisees; till his only hope is somehow or other to have captured one criminal and kept him safe and sane under his own hat.

Am I correct in understanding that Father Brown (the speaker of this quote) is saying that rather than disparage other "criminals," the one criminal that matters is himself (earlier he says entering into the mind of a criminal helps him to solve cases)?

What does it mean to keep this criminal "safe and sane" under his own hat? To make sure that he manages himself as a criminal first, before pursuing other criminals?

Answer 1

To the best of my understanding, Father Brown's quote (in its entirety) would ask that one first deal with my oneself. He would not have you deal with just yourself rather than others. He would have you deal with yourself before you deal with others so that you may understand the darkness within ourselves and also to be compassionate when dealing with others.

In this sense to keep oneself safe and sane is to keep ones decisions and darkness in check.