With the Adepts, An Adventure Among the Rosicrucians, by Franz Hartmann [1910]

VI - THE ALCHEMICAL LABORATORY

https://www.sacred-texts.com/sro/wta/wta08.htm

To make this plain to you, know that each occult symbol and sign, from a mere point up to the double-interlaced Triangle, to the Rose and the Cross, has three significations. The first is the exoteric meaning, which is easily understood; the second is the esoteric or secret signification, which may be intellectually explained; the deepest and most mysterious one is the third, the spiritual meaning, which cannot be explained, but which must be spiritually experienced within yourself. This practical, internal experience is arrived at by the power of intuition, or the faculty by which the soul feels the presence of things which one cannot see with the bodily senses. If a person once feels interior things with his heart, sees them by his internal sight, and understands their attributes, then such a person has become illuminated, and is practically an Adept.