Be not too hasty to trust or admire the teachers of morality: They discourse like angels but they live like men.—Samuel Johnson
Commentary: It is so important to get to know a person, not just assume they are as they seem.
Someone may say all the right things, but that does not mean they believe it. They may be trying to win your trust, so they can use you in some way. It is often those who want to do the most harm, who try the hardest to seem trustworthy, and what better place to do harm than somewhere that requires a premium on trust, such as a church or school.
Or perhaps they are very sincere about what they say, but because of an inner urge, they do bad things anyway. An example of this is priests and preachers who preach one way, but live a different way. Not all bad people want to be bad, they just don’t understand how to be good, or they cannot stop themselves from being bad.
The point is that it is not just what people say that matters, it is what they do.