The correct posture put your hands in the right position and the club at the right angle at address. Look at picture #1 the spine angle represented with the yellow line in this picture is at 43 degrees. The back is bent over more which pushes the arms further away from the body. This puts the hands further away from the body and outside of the shoulders and results in the club being too far away.
This incorrect hand position increase tension in the shoulders and restricts the ability to make a full turn. Compare the different angles from the shoulders to the hands in these two pictures. In Picture 1 The red line shows the hands further away and outside the shoulders. The arms are at an 85 degree angle.
In picture 2 the arms are at a 90 degree angle resting without resistance and tension under the shoulder line. Picture 2 also shows a better spine angle at 48 degrees. The taller spine angle allows the arms to hand directly under the shoulders and closer to the body. Compare the gap between the arms and body on these two pictures. Picture 2 has better posture reducing the stress on your back and shoulders, creates a bigger turn with the body and improves your ability to swing the club on the correct plane. This will all result in a better more consistent golf swing.
Improve your posture at address and improve your golf swing. Your address position is very important in allowing you to make a repeatable golf swing.
The 48 degree spine angle on Picture 2 continues right through the back into the neck. Your head should be up, chin away from your chest and on the same angle as your back.
Work on your posture to relieve back and shoulder pain and improve your golf swing.