People preach all day long and are complete hypocrites. They say one thing and then do another. Also, preaching means that you are talking at someone. Teaching means you are interacting with someone.
When you get someone to agree with you about a subject, they have bought into it. They are more likely to behave accordingly. If you preach at them and they have not bought into what you are saying, you have become, as the Paul says in the New Testament: “As sounding brass, or a tinkling cymbal.” It’s all noise with nothing real behind it.
We have seen the evangelical preachers crash and burn after they have preached hellfire for people’s sins and turn around and do the very thing they preach against. Preachers such as Jerry Fallwell and Jim Bakker were brought out in the light of the public eye and their hollow words showed them to be con artists. They preached but what did they teach?
Teaching is an unselfish act that bears in mind the good and gaining of the student. Preaching is about telling people what to do and can come from the egotism of the preacher. David Koresh held his congregation captive for hours, sometimes days, listening to his end-of-the-world fearsome sermons. He declared himself to be God. And as such, he knew better than anyone else.
A true teacher gives students room to discover things on their own. Their actions are based, not on what they have been told, but what they agree to be right within their own minds and hearts.