You will notice in this picture how close the butt of the racquet is to the ball which prevents the arm swinging and much easier to engage the shoulder to do the swinging then the rest of the arm will follow after the shoulder.
If your a beginner one of the most common intructions you will hear from a coach will be to "SWING your racquet", "swing faster. The problem is that this usually encourages the dominat use of the arm and the rest of the body gets neglated which brings all sorts of problems.
The classic problems that start to happen are hitting late more often, no touch, harder to achieve topspin, inconsistent swing path, arm injuries, sqeezing the racquet too tight to try and increase the racquet speed ect.
"Swinging produces a raw uncontrolled collision with the ball", Doug King, Tennisone.com
A more effective instruction would be to "stroke the ball" much like how someone uses a pool cue.
Tennis is based on using the larger muscles to connect the racquet onto the ball whilst the arm and hand come along for the ride. You want the most mass moving the ball so when the legs and shoulders turn faster on the ball the elbow, hand and racquet all shoot out to fire passively for effortless speed and control on the ball.
Everything happens very close to the ball so the closer the butt of the racquet starts to the ball the lower chance of swinging and then your able to accelerate the racquet through the mass of the larger muscles groups. so you want to change the impulse to grabing the ball instead of hitting the ball.
I like to finsh with these thoughts from one of my coachng resourses that i think you will appreciate -
(In fact, a player who only uses the arms and hands for power would be quickly identified as someone with beginner-like strokes. Advanced strokes require the involvement of body parts other than the hands and arms to be able to play consistenly with control and power. Ultimately, one of the best measures of skill and one of the most important facets of improvement is the ability to relax the hand while hitting strokes thus doesnt encourage swinging with the arm)