Chapter III.—Genesis I. 3,—Of “Light,”—He Understands as It is Seen in the Spiritual Creature.
4. But what Thou saidst in the beginning of the creation, “Let there be light, and there was light,” 1176 I do not unfitly understand of the spiritual creature; because there was even then a kind of life, which Thou mightest illuminate. But as it had not deserved of Thee that it should be such a life as could be enlightened, so neither, when it already was, hath it deserved of Thee that it should be enlightened. For neither could its formlessness be pleasing unto Thee, unless it became light,—not by merely existing, but by beholding the illuminating light, and cleaving unto it; so also, that it lives, and lives happily, 1177 it owes to nothing whatsoever but to Thy grace; being converted by means of a better change unto that which can be changed neither into better nor into worse; the which Thou only art because Thou only simply art, to whom it is not one thing to live, another to live blessedly, since Thou art Thyself Thine own Blessedness.
Compare the end of chap. 24 of book xi of the De Civ. Dei, where he says that the life and light and joy of the holy city which is above is in God.