Bright Hub has a good list of themes from Elie Wiesel's Night. Some, including some I came up with on my own, are the following:
1. The danger of silence
2. Denial and our acclimation to evil
3. Remembering what happened and vigilance so people don't fall asleep to evil as Hitler knew people did in the face of the genocide of the Armenians.
4. Theodicy, evil and evil's challenge to faith in God
5. Dehumanization
6. The loss of innocence
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