Someone challenged me to translate the phrase "You must not fear" into my conlang, and I was stumped, because I couldn't pin down the modality of the phrase. I came up with a phrase meaning "You are obligated not to fear", but it clearly doesn't mean that. It's not a command in the traditional sense, nor specifying an obligation; it's more like a reassurance...
What modality does this phrase have? Are there any crosslinguistic parallels that would help me to understand this construction?
Edit: the passage is from Dune:
I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.
Source: Dune by Frank Herbert