In the Worship of the Shalems, the Lord comes forth from the Holy of Holies to clothe the shalems and administer the feast of bread and wine. He is Melchizedek, the king of rightenousness and the shalem king, and the shalems have come through the valley of the shadow of death to reach him. The moment of his coming is the light seen by those in darkness, in the shadow of death. It is the shining forth of the King of Heaven.
This was the moment when the veil parted and the high priest came out in his robes. The light from the Holy of Holies (which is where the evidence of the visionary men consistently places the light and the tree) shines forth behind him. This was the visionary men's ritual prophecy of the Lord's earthly birth, when Yahweh would come in person to administer the feast of bread and wine to his followers. This is the imagery John uses to report that the prophecy was fulfilled... and the people in darkness and the shadow of death didn't understand what they had witnessed.