The balance and feel of a golf club are transmitted to the player through the hands. Few golfers understand as clearly as they should which parts of the palm and fingers do the actual gripping. To put it another way, they remain hazy about which muscles of the hand hold the club, exert the pressure and, by their position and action, initiate the golf swing and influence its execution.
In regard to the left hand's grip on the shaft, I should like to propose that a golfer think for a minute about the way he picks up a pitcher of water. The last three fingers of your hand grip the handle of the pitcher. They're the ones that lift it and hold it. The thumb and index finger, however, are relaxed—you could hold a pencil or a golf ball between them and your grip on the pitcher wouldn't be affected. That is how you should grip the golf club with the left hand. The last three fingers provide the power to lift and swing the club; they remain glued to the shaft. The thumb and index finger are applied to the shaft much more lightly. They provide as little or as much pressure as is necessary on those shots where touch is important.
from GRAHAM ROSS, Dallas Athletic Club C.C.