Examination of the works of Johann Arndt (1555-1621), a Lutheran author of edifying literature, reveals an understanding of piety based on natural theology and influenced by Florentine neo-Platonism, Paracelsus, Paracelsianism, and the alchemy of Heinrich Khunrath. The present study traces the relevant lines of this tradition with close reference to the sources and analyzes the way in which they were interpreted by Arndt and incorporated into his writings. It closes with a systematic discussion of the coherence existing between nature philosophy and mysticism in the early modern age.