Were there people who advocated worshipping unknowable gods?
Arguably. The main one I could find was this:
St. Augustine - "A God understood is no God at all."
Though I remember at least once being told that God's "mystery", that is, the inability to figure him out, understand him, or be absolutely certain he's there, was part of a reason to worship him.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.