When the golf club is at the top of the swing, it has resistance to movement. If you were to apply your arms to soon, they wouldn't add much speed. Once the body gets the club moving, then the club has less resistance, and so when the arms apply force, they are able to contribute much more speed. Use the body to get the club moving during transition, and then learn to push with the legs and the arms during the release phase. This is another way of thinking about not spinning from the shoulders.