by St. Nikolai Velimirovic
First - because our faith is light. Christ said "I am the light of the world" (John 8:12). The light of the vigil lamp reminds us of that light by which Christ illumines our souls.
Second - in order to remind us of the radiant character of the saint before whose icon we light the vigil lamp, for saints are called "sons of light" (John 12:26, Luke 16:8).
Third - in order to serve as a reproach to us for our dark deeds, for our evil thoughts and desires, and in order to call us to the path of evangelical light; and so that we would more zealously try to fulfill the commandments of the Savior: "Let your light shine before men, that they may see your good works" (Matthew 5:16).
Fourth - so that the vigil lamp would be our small sacrifice to God, Who gave Himself completely as a sacrifice for us, and as a small sign of our great gratitude and radiant love for Him from Whom we ask in prayer for life, and health, and salvation, and everything that only boundless heavenly love can bestow.
Fifth - so that terror would strike the evil powers that sometimes assail us even at the time of prayer and lead away our thoughts from the Creator. The evil powers love the darkness and tremble at every light, especially at that which belongs to God and those who please Him.
Sixth - so that this light would rouse us to selflessness. Just as the oil and wick burn in the vigil lamp, submissive to our will, so let our souls also burn with the flame of love in all our sufferings, always being submissive to God's will.