Joy!!

King David (Dovid Hamelech) in Tehillem (Psalms) advises us, "Serve G-d with joy, come before Him with jubilation."

G-d attaches a great deal of importance to joy, as it says in the Talmud "The Divine Presence rests only upon one who performs a mitzva in a joyous spirit." In fact, it is said about the famous Kabalist, Rabbi Yitzchak Luria, that he merited Divine inspiration and even got to meet Eliyohu Hanavi (Elijah the Prophet), because he infused his mitzvot with so much joy.

The Tzemach Tzedek (the third Chabad Rebbe) once advised someone who found it difficult to be happy, he told him: "Thought, speech and action are within one's control. A person must guard his thoughts and think only thoughts that bring joy. He should be cautious not to speak about sad or depressing matters. And he should behave as if he were very joyous, even if he doesn't feel especially happy. In the end, he will ultimately be joyous."

It says that Rava would begin his lesson with a humorous remark so that his students would be cheerful and that way more receptive and better able to understand the lesson.