A person can accomplish many things as part of his routine or out of a sense of duty.
But sometimes he undergoes such a severe state of spiritual or physical exhaustion that he cannot act.
He must experience what the author of the Tanya refers to as “joy of the heart” in order to purify and illuminate his soul.
This kind of joy – genuine, heartfelt joy not frivolity – is the optimal state of the soul.
When a person experiences this joyful, positive state of mind, all of his actions are animated and effortless.
He solves problems and meets challenges, and new paths open up for him.
Rabbi Adin Steinsaltz