From the Gospels
And after six days Jesus took with Him Peter and James and John, and led them up a high mountain apart by themselves; and He was transfigured before them, and His garments became glistening, intensely white, as no fuller on earth could bleach them. (Mark 9:2-3)

“No one, when he has lit a lamp, puts it in a secret place or under a basket, but on a lamp stand, that those who come in may see the light. The lamp of the body is the eye. Therefore, when your eye is good, your whole body also is full of light. But when your eye is bad, your body also is full of darkness. Therefore take heed that the light which is in you is not darkness. If then your whole body is full of light, having no part dark, the whole body will be full of light, as when the bright shining of a lamp gives you light.” (Luke 11:33-36)
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The lamp of the body is the eye. If therefore your eye is good, your whole body will be full of light. But if your eye is bad, your whole body will be full of darkness. If therefore the light that is in you is darkness, how great is that darkness!” (Matthew 6:22-23)

Account of St Seraphim’s Transfiguration
A close admirer and follower of St. Seraphim, Motovilov, described the miraculous transfiguration of the starets’ face. This happened during the winter, on a cloudy day. Motovilov was sitting on a stump in the woods; St. Seraphim was squatting across from him and telling his pupil the meaning of a Christian life, explaining for what we Christians live on earth.
"It is necessary that the Holy Spirit enter our heart. Everything good that we do, that we do for Christ, is given to us by the Holy Spirit, but prayer most of all, which is always available to us," he said.
"Father," answered Motovilov, "how can I see the grace of the Holy Spirit? How can I know if He is with me or not?"
St. Seraphim began to give him examples from the lives of the saints and apostles, but Motovilov still did not understand. The elder then firmly took him by the shoulder and said to him, "We are both now, my dear fellow, in the Holy Spirit." It was as if Motovilov’s eyes had been opened, for he saw that the face of the elder was brighter than the sun. In his heart Motovilov felt joy and peace, in his body a warmth as if it were summer, and a fragrance began to spread around them. Motovilov was terrified by the unusual change, but especially by the fact that the face of the starets shone like the sun. But St. Seraphim said to him, "Do not fear, dear fellow. You would not even be able to see me if you yourself were not in the fullness of the Holy Spirit. Thank the Lord for His mercy toward us."
Thus Motovilov understood, in mind and heart, what the descent of the Holy Spirit and His transfiguration of a person meant.

Based upon everything that was discussed in the retreat, these scriptures, and the excerpt from the Life of St Seraphim, define the phrase, “Let Your Light So Shine.” What is the light? Where does it come from? How do you let it shine?