Sleep is often a poetic euphemism for death; Utanapishtim even says as much when Gilgamesh finally catches up with him... "How alike are the sleeping and the dead..." In any event, Gilgamesh's foreboding deepens as they face the entrance to the forest. Gilgamesh and Enkidu find and confront Humbaba, and Humbaba tries to pursuade Gilgamesh to make friends with it, but Enkidu advises him to kill it, for fearing the wrath of Shammash. Gilgamesh is having second thoughts about killing Humbaba, but Enkidu turns his ear and they do end up killing the monster. Of course, this angers all the gods except Shammash, who are finally provoked past the limits of patience when the duo kill the Bull of Heaven which Ishtar petulantly lets loose on Uruk. However, unable to bring themselves to kill Gilgamesh, they focus on Enkidu instead and inflict him with a long terminal illness.

So it is ironic that Enkidu who wisely suggested that Humbaba was a terrifying force best left alone inadvertently goaded Gilgamesh into a course of action that would lead to his (Enkidu's) death. Ancient Mesopotamian literature is replete with such ironies. After having adventures in the Cedar Forest and even slaying the Bull of Heaven and earning Ishtar's ire in the process, their last adventure is spent waiting for Enkidu to die. Enkidu is clearly terrified of death and suffers terribly while Gilgamesh keeps a horrified watch by his bedside as his friend sinks ever lower. After Enkidu's death, Gilgamesh fairly loses his mind and orders a statue of Enkidu to be made and installed on a couch next to the royal throne.

Gilgamesh mourns over Enkidu the same amount of time Enkidu is in the throes of passion with Shamhat, and the same as the duration of Utanapishtim's flood. After failing to get immortality for himself, Gilgamesh is presumably saved from an ignominious return by Utanapishtim's wife, who suggests giving him something so he doesn't go back to Uruk empty-handed. Utanapishtim tells him about a secret plant that can return him to respect, the Epic not only is the story of an individual man's struggle with himself, but of humanity's struggle to achieve something approaching civilization when burdened with such monumental troubles.
Abusch (2001) states that though the protagonist/antagonist relationships vary across the different versions of the Epic, its fundamental theme remains the conflict between the extraordinary and the mundane. Gilgamesh is afflicted with ordinary human worries but has extraordinary adventures in the process of addressing them. The literary themes themselves within the Epic are there just to facilitate the hero's grappling with the facts of life.

Jager (2001) describes the theme in the Epic as essentially the separation of man from the animals, which occurs in two examples, namely Gilgamesh and Enkidu. Enkidu starts out as an unrefined savage who gradually becomes a cultured human being.

It tells how a natural creature that ate grass and roamed the steppe learned to inhabit the city and how someone who lived with a herd of wild gazelles became the favorite companion of a king. The Epic of Gilgamesh tells the story of how a headstrong and selfish young king gradually became transformed into an exemplary and wise ruler." Jager (2001).

Clearly, since art is in the eye of the beholder, there are numerous ways the Epic can be interpreted.

Bibliography

Abusch, Tzvi. (2001). "The Development and Meaning of the Epic of Gilgamesh: an Interpretive Essay." Journal of the American Oriental Society 121.4: 614-622.

Jager, Bernd (2001). "The Birth of Poetry and the Creation of a Human World: an Exploration of the Epic of Gilgamesh." Journal of Phenomenological Psychology. 13.2: 131-154.

Carnahan, Timorthy (ed). "The Epic of Gilgamesh." March, 2005 http://www.ancienttexts.org/library/mesopotamian/gilgamesh