Sin, Pollution & the Anger of God
Sickness meant a god was angry — perhaps for a sin you could not even name.
Also: sin · arnu · anger of god · divine anger · unknown sin · impurity · guilt · confession
When trouble struck — illness, loss, bad luck — Mesopotamians often read it as a sign that they had offended a god, knowingly or not, and that their protective deity had withdrawn in anger, leaving them open to demons and disease. The offense might be a moral fault, a ritual lapse, or a transgression one never realized one had committed. Relief came through confession, prayer, and the rites of the exorcist, which identified the cause, appeased the god, and lifted the impurity. The poignant theme of the 'unwitting sin' — being punished for a fault one cannot even name — runs through the wisdom and prayer literature.
In short
The understanding of misfortune as caused by sin or impurity (known or unknown) that angers one's god and exposes one to harm, and which must be removed by confession and ritual.
Where it’s found
'A man and his god' (ETCSL 5.2.4, in corpus); Ludlul bēl nēmeqi II; the penitential prayers (akkadian-pending)
How the idea developed across Sumer, Babylon & Assyria
The 'unknown sin' theme is sharp in Ludlul and in the šuilla/dingiršadabba prayers (akkadian-pending); the Sumerian 'A man and his god' already voices the abandoned sufferer (in corpus). The line between moral fault and ritual impurity is fluid in Mesopotamian thought.