Zarathustra's shadow sings about a time when he was in the Orient—far from Europe—and surrounded with all sorts of delights.
Zarathustra steps outside again and is pleased that his companions and he have chased away the spirit of gravity. But then he sees them all inside, praying to the king's ass (donkey).
Zarathustra leaps in and chastises his guests for praying to the ass. However, he takes this as a good sign, since it shows that they are convalescing.
They all step outside into the cool night and the ugliest man says that for the first time he is satisfied with his entire life. The others agree and all turn to Zarathustra in gratitude. Zarathustra sings a song that in many ways is the culmination of the entire book. The world is very deep, full of deep sorrows and deep joys. But while sorrow and suffering want people to aim for something else, joy wants only itself for all eternity. Because all things in the universe are intimately connected, we cannot wish for an eternity of joy without wishing for the suffering that accompanies this joy. "Joy wants the eternity of all things, wants deep, wants deep eternity."
Zarathustra rises the next morning and finds a lion outside his cave, which he takes to be a sign that the overman is coming. Zarathustra rises triumphantly, realizing he has overcome his final sin: pity for the higher man.
Part IV is lined with the pervasive irony and humor that we should expect from a book that is constantly praising laughter. In the first nine chapters, we see all sorts of caricatures that are meant in part to poke fun at Nietzsche himself. The last eleven chapters contain even more light-heartedness, which reaches its epitome in the delightfully frivolous song by Zarathustra's shadow.