The question is: must one practice what one preaches? And this question is as old as it is new. Intuitively, an unequivocal “yes” should be the response here, yet this question is raised day and day again. Let’s get into why. First, though, I’ll offer what I take to be the simplest reasons in favour of doing what you say as a rule.
You might say that people do two things: practice and preach, or do and say. Of course, there is no such difference. Speech is as much of an act as a kiss or slap to the face. More, we act for a specific purpose, even if that purpose is enclosed in the act itself.
For instance, some people go to the gym to become healthier; others go to look good. Others will go for the sheer thrill of squatting a plate more than they did yesterday. In either of these cases, we have a specific project that we’re involved in when we act, and a lot of other things go into that project besides “going to the gym.” If the project is to become healthy, eating well is automatically involved, as well as mental health, etc. Something very specific is being done, and it’s my position that all acts work this way.
This includes speech acts. Excluding for the time obvious speech acts (promises, apologies, marriage proclamations, court rulings — these are things that only exist if they are said), let’s talk about this act of “preaching.” Let’s say further that when one preaches, one is ultimately trying to convince others of something. Then preachers have a project in the same way that the gym goer does: “today, I’m going to make my body healthier” translates to “right now, I’m going to convince people that my ideas are correct.”
In the same way that eating healthy is a component of the gym project, a number of other things go into the project of convincing people. This includes whether or not the preacher is a hypocrite. It makes sense: you wouldn’t say that someone actually goes to the gym to be healthier if after every workout they knock back a Big Mac. You’d say that they go to the gym for some other reason. The same holds for preachers. If a preacher consistently goes against what they say, then we know that we have no reason to be convinced by them. They haven’t convinced themselves, it seems. So we say things like, “they just want attention,” etc. — and rightly so.
So we should practice what we preach for the same reason that builders shouldn’t swing a sledgehammer at a house they’ve nearly finished. It’s simply counterproductive.
Yet so many people are hypocrites. I attribute this to the fact that people simply change their views over time. I may have started going to the gym to be healthy, but maybe I ended up going to meet people. If at the outset I preached healthiness as my aim, then it sure looks hypocritical when I slacken my diet. The point is that I look hypocritical to others, not myself. Others don’t know that my views have changed. This is where the problem lies.