My words shall not pass away

Nothing of this world is more durable than the heavens and the earth, and nothing in the order of nature passes away more quickly than speech. Words, as long as they are incomplete, are not yet words. Once completed they cease utterly to be. In fact they cannot be perfected except by their own passing away. Therefore he says: Heaven and earth shall pass away, but my words shall not pass. As if he were openly to say: all that seems to you enduring and unchangeable is not enduring and without change in eternity. And everything of mine that seems to pass away is enduring and without change. My speech, that seems to pass away, utters thoughts (sententiae manentes) which endure forever.

 -- Gregory the Great (540-604 AD), excerpt from HOMILIES 1