Khunrath was a physician trained at Basel, a Paracelsian, and the author of the Amphitheatrum Sapientiae Aeternae, an incomplete version in 1595, the fuller edition posthumously in 1609, which is remembered almost entirely for its engraved plates.
The famous one shows a single vaulted chamber divided between an oratory, where a bearded figure kneels at a tent-altar under a Hebrew inscription, and a laboratory crowded with furnaces, alembics and instruments, with a music-strewn table between them. The motto attached to the workbench states the doctrine in six words: without divine inspiration no man is great. Prayer and furnace-work are not two activities but one, and the alchemical operation cannot succeed without the operator's sanctification.
That fusion, Lutheran devotion, Paracelsian chemical medicine, and Christian Kabbalah, with Christ identified as the stone of the philosophers, is why he is treated as a forerunner of the Rosicrucian manifestos that appeared a few years after his death, though he founded nothing and joined nothing. The Sorbonne condemned the Amphitheatrum in 1625.
Modern occult writing tends to treat his plates as coded diagrams of a psychological or purely spiritual process. Peter Forshaw's scholarship has argued the opposite and more interesting case: Khunrath meant the laboratory literally, was a practising chemical physician, and the spiritual reading that detaches his alchemy from actual furnaces is a later imposition on him.