Gods in both Greece and Mesopotamia are concepts that represent the most significant aspects of the world. Mesopotamian Gods are egos and wills and nothing more, they exist entirely on a supernatural level. They cannot be perceived, only talked about, and without a priest you probably would't be aware of them at all. There was no nature in historic Mesopotamia, only will. And so the actions of the Mesopotamian Gods are completely arbitrary, they never have to answer to what the Greeks would call, "natural laws." There is in fact no nature in historic Mesopotamia (prehistoric Mesopotamia might well be another story), and that is why the Mesopotamian hero, Gilgamesh, was considered heroic when he tried to kill Death. In Mesopotamia Death and Fate were never natural but always something that had been willed, something that had been arbitrarily imposed upon us by egos and wills just like out own but immeasurably more powerful. Gilgamesh could be admired for opposing such a will, because the idea that God was Good hadn't been invented yet.
For the Greeks, concepts representing the most significant aspects of the world had to be supernatural egos as in Mesopotamia, but alongside of that these same concepts also had to be thought of in immediate and perceivable terms. Aphrodite for example, was a supernatural Goddess with an arbitrary will, but she was also something completely real that no one needed a priest to understand. Gilgamesh threw a slab of carrion in the face of Inanna, the Mesopotamian Love Goddess, but no one would think of doing that to Aphrodite. No one thought of defying Aphrodite in such a way, because no one ever thought of submitting to her. She was as close as one's blood and as close as one's life. It makes no sense to either defy her or submit to her, she is simply part of our lives. Achilleus lived in a world where Nature and Fate was stronger than the will of any God, and the Greeks would say it again and again: Fate is stronger than God. Achilleus was heroic specifically because he did not rebel against Fate, an action like that of Gilgamesh would have made no sense to him.
There had never been anything like Nature in historic Mesopotamia, nothing simply was, everything was as God willed it. Sometime around 1500 BC, while Mesopotamia was ruled by foreigners, the idea developed that the Gods, and increasingly God, was completely Good, and that bad things happened because people were not sufficiently obedient. Heroic rebellion ceased.
In the later Greco-Roman world it came to be considered aberrant, sinful or at least pointless to rebel against authority, divine or secular, but natural to rebel against Time and Fate. Both Achilleus and the classic Greeks considered it aberrant, grotesque or at least pointless to rebel against Time and Fate, but natural to rebel against authority.
The all-powerful Mesopotamian Gods spent most of their time in a state of unknowing quiescence. The anthropomorphic Gods of the Iliad, which probably took that form due to Mesopotamian influence, had enormous power but nothing of any real significance to effect. They spent most of their time watching the equivalent of soap operas and football, and that was their life. Humans living that way would be considered hollow and insignificant. If you eliminated them from the Iliad altogether, they would not be missed.
In Mesopotamia, the power of immortal, invulnerable beings was the only power that mattered. If nothing is real but will and intention, then the only power that matters is the power to be God. The whole idea in Mesopotamia, and in the Middle East in general was to identify oneself with that which was immortal and invulnerable, to share in the God's power and to become as Godlike as possible; perhaps to become completely Godlike, to escape Death and pain forever. In Mesopotamia power was not valued to the extent that it was human, human beings were valued to the extent that they had power or were connected with power. Regrettably, this still passes for right and wrong today.
On the other hand, the literature of the classic Greeks was fairly consistent in its ideal of right and wrong. The man who acts properly, acts according to his Nature, regardless of what will or will not lead him to power in the Mesopotamian sense. For much of the classic age no one could say this, because you canít think about Nature, especially your own, as a deity with an ego, and the archaic Greeks had to think about all concepts as supernatural egos as well as aspects of Nature. It is not until the end of the Fifth Century that we find a character like Philoktetes (Philoktetes, 874, 902-903, 950) who acts exactly as Achilleus, Orestes, Oedipus and the others had acted all along and who is actually named as one who acts according to his physis, Nature. Just for a brief moment there were still people who understood the ancient concept of morality that we see in Homer, etc., and there was no longer a need felt to deify concepts, and for that one moment someone like Sophokles can say that a character like Philoktetes is acting rightly because he is acting according to his Nature, because he is being human.
The Gods in the Iliad have achieved superhuman, supernatural power, and they are completely trivial. The power expressed in the Iliad comes from weakness, vulnerability, the certainty of failure, of Death, and precisely from the limitations of our effective power. It is this power, which the classic Greeks recognized as Sacred, that is the source of all significance, and it is this power that makes us human.