In a good golf swing the body only rotates at approximately 2.5 mph. If the body doesn't turn very fast and it's telling the arms how fast to come down the overall swing would appear slow and effortless.
Most people are confused when they see someone with this type of golf swing. They just can't figure out how they do it no matter how much golf instruction they have taken. If this is you, what you are missing is that the body is telling the arms how fast to come down.
The power is generated through the club hinging and re-hinging in the wrists. The looser the wrists, the more club head speed that is generated. If you've ever had some golf instruction or lessons in the past you will have worked on your wrist hinge but in doing so you were most likely trying to hit the ball solely with your arms. This hitting tightens your wrists and actually slows the club down.
To get this easy look you need this looseness in the wrists and you get it by not trying to hit anything at all. In other words, you're just letting the arms go along for the ride.