2 Corinthians 4:6

For God... hath shined in our hearts. In the account of the creation of the world given in Genesis, light is said to have been created first of all, because light is a quality most splendid, pleasant, gladdening, useful, efficacious, and powerful. Cf. Dionysius (de Divin. Nomin. c. iv.), who enumerates thirty-four properties of light and of fire wonderfully adapted to set forth God and the things belonging to Him. Cf. note to Genesis 1:2.

Hugo (de Sacram. pag. i. c. 10) and others point out, by way of allegory, that on the first day, when light was created and divided from darkness, the good angels were established in good and the evil in evil, and were separated each from other. What, therefore, was done in the world of sense was an image of what was being done in the unseen world. Nay, S. Augustine frequently maintains that the literal sense is that which refers to the angels.

The Apostle here explains this light tropologically. As God formerly produced light out of darkness, so now has He made unbelievers into believers, and has enlightened them with the light of faith. So, too, S. Augustine (contra Advers. Leg. lib. i. c. 8) lays down that by light and day succeeding the pre-existing darkness, and being again succeeded by darkness, is signified what spiritually takes place in man, viz., grace succeeding sin, and sin again grace.

To give the light of the knowledge of the glory of God in the face of Jesus Christ. To illuminate us, that we in turn may illuminate others with that clear and glorious knowledge which shines forth from God in the face of Christ, or else by means of our clear knowledge of Christ and His redemption. It is commonly said that a man is known by his face; hence to know "in the face" signifies to know clearly and openly. Just as at night a lighted torch throws light on the surrounding darkness, and is carried before travellers to show them the way clearly, so does Christ lighten us in the night of this world, so that we know God surely and plainly, and go on our way to see Him in the life of bliss in heaven. Hence the Glossa symbolically explains these words to mean: by Jesus Christ, who is the Face of the Father; for without Him the Father is not known. There is still kept up an allusion to the veil over Moses' face contrasted with the open face of Christ (iii. 15). The word face may be, with the Syriac, translated the person, i.e., we illuminate, others in the name, place, and authority of Christ. S. Cyril (de Fide ad Theodor. Imp.) says. "He hath shined in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ. See how openly and plainly the light of the knowledge of God the Father has shone, forth in the person of Christ."