Angel Bearing the Keys to the Mysteries, illustration in Albumazar(?) or Herpentilo Pareja, Albamasia sive [magia] naturalis et innaturalis, ms., 17th century, Verginelli-Rota Collection, Accademia dei Lincei, Rome. The angel who holds the keys to the mysteries indicates that this knowledge is forbidden to whoever cannot possess them. — Alchemy: The Great Secret, Andrea Aromatico, “Abrams Discoveries” series. Harry N. Abrams, 1 May 2000. Image at p. 65. The key of mysteries is also one of the attributes of the archangel Raziel.
Original public domain image from Wikimedia Commons