Let us then throw off the works of darkness and put on the armor of light.
– Romans, 13:11-14

Here is Thomas Merton in Seven Storey Mountain:

When a ray of light strikes a crystal, it gives a new quality to the crystal. And when God’s infinitely disinterested love plays upon a human soul, the same kind of thing takes place…The soul of man, left to its own natural level, is a potentially lucid crystal left in darkness. It is perfect in its own nature, but it lacks something that it can only receive from outside and above itself. But when the light shines in it, it becomes in a manner transformed into light and seems to lose its nature in the splendor of a higher nature, the nature of the light that is in it.

And Elisabeth Kübler-Ross:

People are like stained-glass windows. They sparkle and shine when the sun is out, but when the darkness sets in, their true beauty is revealed only if there is light from within.

One more. This is from Let Us Be What We Are by Clarence J. Enzler:

Each piece in that mosaic is different; ordered to contribute a certain color, shape or background to the whole design. This piece reacts to the light so as to reflect redness; this one, blueness, this, yellow; this purple; this brown. So, with each of us. We are to react to the light of God’s grace so as to reflect Christ, to reflect Him not only to the world but to the sight of God Himself. We are, each of us, a piece of the Father’s mosaic of the Christ. So it is with us in the divine plan, we who are all bits of the mosaic of Christ on earth. When one of us fails to reflect his or her portion of the image of Christ, the gap is so noticeable that God the Designer, Our Lord of the Good Shepherd, must leave the 99 or the 9,999 pieces are in place and go seeking for that which is lost.