"IN order to understand the meaning of religion, we must know the etymology of the word. St. Augustine, in his book De vera religione considers it to be derived from "re-ligare" (to re-bind). One thing is bound to another, when it is so joined to it, that it cannot separate from it, and unite itself to anything else. The word "re-binding", however, implies that one thing, though united to another, has begun, in some degree, to disconnect itself from that other. Now every creature existed, originally, rather in God than in itself. By creation, however, it came forth from God, and, in a certain measure, it began, in its essence, to have an existence apart from Him. Hence every rational creature ought to be reunited to God, to whom it was united before it existed apart from Him, even as “unto the place whence the rivers come, they return to flow again” (Eccle. i.). Therefore, St. Augustine says, (De vera religione), “Religion reunites us to the one Almighty God.” We find the same idea expressed in the commentary of the Gloss, on the words, “for of Him, and by Him” (Rom. xi. 36)."
~St. Thomas Aquinas: Liber contra impugnantes Dei cultum et religionem, Part I.
