- Obscurity, speaking in fables, non-clarity, indirectness. Multiple layers to one's teaching. This possibly for the sake of pedagogy.
- Teachings for the public versus teachings for the initiates/elite/true disciples. Two contradictory or opposed layers to one's teaching.
The former and the latter are quite different, and I wonder whether the latter might be far less common than the former.
It seems clear that some thinkers, particularly in ancient Greece and Rome, had opposed esoteric and exoteric aspects to their work, and that we should acknowledge and try to discern this where it exists.
But I'd question whether esotericism is "of the greatest importance for our understanding of the whole course of Western philosophy". The author seems to think of it almost as a kind of skeleton key, as though maybe there is a significant stream of thought that people have radically misunderstood. The idea of a hidden thread of elite, secret knowledge has an alluring, conspiratorial feel to it that the author doesn't mention -- a vibe that is not so foreign to our modern sensibilities (Scientology, Kabbalah, New Age, ...).
Melzer writes that "with pedagogical esotericism, the writer actually embraces concealment and obscurity (of the right kind) as a positive good and as something essential to the primary purpose of his act of writing: philosophical education". How does this not describe art of all kinds -- e.g. fiction writing -- where the creator has a didactic purpose, but artfully weaves this into their work? ("Ars est celare artem.") Again, there is no distinction made between nonclarity and the demand for active, engaged, creative reading and thinking on the one hand, and on the other, radically opposed esoteric and exoteric meanings.