If you think about your body for a minute, you know that it moves much slower than your arms in real life.  So if your body can’t turn all that fast, how do you get a fast looking golf swing?  You get a fast looking golf swing when you try to hit the ball as hard as you can with just your arms.  This means that your arms are moving independently from your body. 

What happens to your shots when your arms outpace your body?

First, won't make solid contact with the sweet spot on the clubface because swinging with your arms alone will cause you to manipulate the clubface as it swings through impact.

Secondly, the harder you swing, the tighter your wrists and arms will be through impact.  Tighter wrists release slower than looser wrists and looser arms extend more than tighter arms (which increase the width of your swing arc).

To slow down a fast looking golf swing, we first have to think logically about it.  Pros have a slow looking swing and they hit the ball a long way and you have a fast swing that hits the ball shorter.  So why do you insist on hitting the ball harder than the pros do?  Unfortunately, human nature usually takes control of us when we go to hit a golf ball.  It says that the harder you swing the further the ball will go.  This does not allow us to see the logic behind swinging slower.  Swinging slower feels like you have less power so you cannot see how you can actually hit the ball better and farther by not using your arms.  You must convince yourself that you must swing slower to hit the ball better.  Once you slow down, you will make better contact in the middle of the clubface, widen your arc and release the club faster.  All of these things add up to more distance with less effort. 

I like my students to try this drill in order to take the arms out of their swing.  All you have to do is hold the club at about waist high and feel your body swing the clubhead.  Remember the clock.  If the post turns faster the arms swing faster.  As you swing, listen to the swishing sound the clubhead is making as it swings through impact.  Now, try to make the club swing faster by shifting your body weight from the right leg to the left leg allowing your body to turn at the same time.  If you let your arms swing freely you will hear the club swish faster as you increase the speed of your body.