Mental illness more than physical illness affects the soul. The soul has three garments which are thought, speech, and action. The soul is above these three garments clothed within them. Mental illness affects these garments, primarily thought but does not pollute the pure Jewish soul. The pure Jewish soul suffers exile under these polluted garments.
Most people neglect the study of the soul and truth.
They are content with life in its simplicity. These topics are deep, confusing, and dangerous. They need to be taught by a Rebbe who has answered the difficult questions which are forbidden to ask. This Rebbe may have himself suffered mental illness before beginning his search for truth. Those that suffer mental illness are forced to look into themselves, to be introspective.