The Only-begotten of God, the Sun of justice, like a huge and brilliant candle has enkindled and enlightened the prison of this world – so that everyone willing to be enlightened can come near him and be united to him so that nothing may come between them and him. Our sins are barriers between us and God. When these have been taken down we are indeed joined to him to be enlightened by and, as it were, incorporated into, the true light. The quenched light is so immediately united to the shining and burning light that it is enlightened – insofar as we can identify the effect of what is invisible by an example of what is visible.
3. At this great and brilliant star let us then, as the prophet says, light for ourselves the light of knowledge before we leave the darkness of this world. If we do otherwise we will pass from darkness into darkness – and everlasting darkness at that. But what is this knowledge? Surely it is to know that the Lord will come, even if we cannot know when he will come. That is all that is asked of us.
Bernard of Clairvaux, Sermons for Advent and the Christmas Season, On the Eve of the Lord’s Birth, Sermon Three: On the Chant: “Today you shall know that the Lord will come” v. 2, 3 (CF 51, p. 61)