[It is with the service of G-d] 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 is stronger than the other. Similarly, 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 [it must be conquered] with alacrity, which derives from joy and an open heart that is unblemished by any trace of worry and sadness in the world.