The proof of this assertion is the fact many people have degenerated intervertebral discs, but no pain. Many doctors are not aware of this fact, and they will point to an x-ray revealing disc degeneration and tell you the cause of your back or neck pain has been found. The vertebrae are held in their proper position in relationship to each other by muscles and by ligaments. Muscles alone are not able to do the job. Nevertheless, they can help, and this is the rational basis of exercise as a treatment for an unstable back or neck.
Strong ligaments are necessary for a stable spine.
However, instability is not, in itself, the cause of pain. The cause of pain is inflammation. Inflammation happens when vertebrae rub against each other in an abnormal way due to the presence of damaged ligaments. This is why anti-inflammatory agents, including cortisone, can result in temporary relief of pain. However, since the underlying condition is not treated with anti-inflammatory agents, this suppression of symptoms is like putting your finger in a dike.