זוהר שמות — דף רח ע”ב

The fingernails in the secret of Havdalah: the fingernails represent other faces that must shine through the candle. The inner fingers without nails are the anterior faces. The outer side of the nail is the lower aspect. The Havdalah candle must have two flames, containing the secret of duality and unity. One who distinguishes between the holy and the mundane, between light and darkness, reveals the secret of the union of the anterior and posterior faces in holiness.