The faithful must be strong through charity, for love is as strong as death (Song 8:6); hence, it is symbolized by a pillar of fire capable of consuming everything: therefore, they received a burning pillar of fire for a guide on the unknown journey (Wis 18:3). As fire makes the surroundings visible, puts metals to the test, and destroys what can burn, so charity enlightens human actions, examines one's motives, and exterminates all vices.
[Thomas Aquinas, Commentary on the Letters of Saint Paul to the Galatians and Ephesians, The Aquinas Institute for the Study of Sacred Doctrine (Lander, WY: 2012) p. 178. From the commentary on Ephesians.]
