Fire has four natures: it burns, it cleanses, it warms, it gives light. Similarly the Holy Spirit burns away sins, cleanses hearts, shakes off sloth and enlightens ignorance. Fire is by nature incorporeal and invisible, but when it takes on a bodily form it appears in various colours, according to the materials in which it is burning. In the same way, the Holy Spirit cannot be seen except through the creatures in which he operates.
--St. Anthony of Padua
