A “signature” was placed on all things by God to indicate their affinities — but it was hidden, hence the search for arcane knowledge. Knowing was guessing and interpreting, not observing or demonstrating.
understood by only a few; obscure; requiring secret or mysterious knowledge
Hyphenation
un·der·stood by on·ly a few; obscure; re·quir·ing se·cret or mys·te·ri·ous knowl·edge