Chapter 14 — Part I: The Creed — Article XII: Life Everlasting
Section 20. An Illustration Of This Truth — These are truths, so divine that they cannot be expressed in any words or comprehended by us in thought. We may, however, trace some resemblance of this happiness in sensible objects. Thus, iron when acted on by fire becomes inflamed and while it is substantially the same seems changed into fire, a different substance; so likewise the blessed, who are admitted into the glory of heaven and burn with a love of God, are so affected that, without ceasing to be what they are, they may be said with truth to differ more from those still on earth than red-hot iron differs from itself when cold.