Commentary for Taanit 43:13

...The Presence of Gd is a called 'joy' and anyone who rejoices for the sake of heaven cleaves to the Presence. In the book Ben Porat Yosef p. 38 he says in the name of his teacher that through joy one moves from smallness to greatness, and these two jesters removes people's troubles in order to bring them closer and lift them up. This was hinted at in the story of the binding of Yitzchak where it says "and lift him up" (Genesis 22:2). This is because it is through holy laughter (tzchok, which is the roots of Yitzchak's name) that one elevates the laughter of youth. It further says "and he took with him two (shnei) youths" (Genesis 22:3) which can be read as he took with him the years (shanim) of youth. See page 99...

When we see sad people, we joke around, etc.: That through this, they merited the world to come; as we say in the chapter [entitled] Nigmar HaDin (Sanhedrin 46a), "When a man is in pain, the Divine Presence says, 'My head is [too] heavy for me, etc.'" See there.