The candles lit before the icons of the Theotokos are a symbol of the fact that She is the Mother of the Unapproachable Light, and also of Her most pure and burning love for God and Her love for mankind.
The candles burning on the altar represent the non-created Light of the Trinity, for the Lord dwells in an unapproachable light. They also represent the fire of Divinity which destroys our ungodliness and sins. The candles lit before the icons of the Savior signify that He is the True Light which lighteth every man that cometh into the world (John 1:9); at the same time, He is a Fire which engulfs and revives our souls and bodies.
You can see that a city is prosperous by the wealth of goods for sale in the market. Land too we call prosperous if it bears rich fruit. And so also the soul may be counted prosperous if it is full of good works of every kind. But first of all it has to be farmed energetically. Then it must be watered by abundant streams of heavenly grace for it to bring forth fruit, some thirty fold, some sixty fold, and some a hundred fold. The soul only acquires goodness and the capacity of fulfilling its duties if it has the grace of God On the other hand, what is uglier or more disgusting than a soul given over to base passions? Look at the hot-headed person: he is like a wild beast. Consider the slave of lust or gluttony: who can bear the sight of him? Pity the victim of melancholy whose spirit is totally prostrated. It is for us to seek to acquire beauty so that the Bridegroom, the Lord, may welcome us into his presence and say, “You are utterly fair, my love, and there is no flaw in you.” (Song of Sol 4:7)
The candles lit before icons of saints reflect their ardent love for God for Whose sake they gave up everything that man prizes in life, including their very lives, as did the holy apostles, martyrs and others. These candles also mean that these saints are lamps burning for us and providing light for us by their own saintly living, their virtues and their ardent intercession for us before God through their constant prayers by day and night. The burning candles also stand for our ardent zeal and the sincere sacrifice we make out of reverence and gratitude to them for their solicitude on our behalf before God.
This day the earth became Heaven for us. Not because the stars descended from the heavens to earth, but because the apostles ascended to Heaven by the grace of the Holy Spirit, which was now abundantly poured forth, and so the whole world was transformed into heaven; not because human nature was changed, but because there was a change in the direction of the will. For there was found a tax-gatherer, and he was transformed into an evangelist. There was found a persecutor, and he was changed into an apostle. There was found a robber, and he was led into Paradise. There was found a prostitute, and she was made the equal of virgins. There were found wise men, and they were taught the Gospels. Evil fled away, and gentleness took its place. Slavery was put away, and freedom came in its stead. And all debts were forgiven, and the grace of God was conferred. Therefore Heaven became earth.