This must be made known as a cardinal principle: Just as it is with a victory over a physical opponent—for instance, two people who wrestle with each other, each striving to fell the other, if one of them is lazy and sluggish he will easily be defeated and will fall, even if he be stronger than the other—so it is with the conquest of one's evil nature: it is impossible to conquer the evil nature with laziness and sluggishness, which stem from sadness and a stone-like dullness of the heart, but rather with alacrity, which derives from joy and an open heart that is unblemished by any trace of worry and sadness in the world.

As for the verse, "In every sadness there will be profit," 1 which implies that some profit and advantage would be derived from it—on the contrary, the wording implies that, the sadness itself has no virtue, except that "there will be profit"--some profit will ultimately be derived from it. This profit is the true joy in G‑d which follows the genuine sadness over one's sins, with bitterness of soul and a broken heart, which must come at specific, suitable times. For through such sadness, the spirit of impurity and of the sitra achra2 is broken, and so too the "iron wall" that separates the person from his Father in Heaven....

The joy that follows such sadness is of a greater quality, similar to the distinctive quality of light which follows darkness. As the Zohar comments on the verse, "And I saw that wisdom surpasses foolishness as light surpasses darkness"...3