The light emitted by the candle symbolizes the light of Christ, the very presence of the Lord in our lives, but also the hope for eternal life, the life as it is called of the inexhaustible light.
As a symbol, the candle functions in the life of the believers as a reductionist, like all other kinds of piety, lighting candles, offering incense
In the Old Testament the god commands Moses to advise his brother as follows
Command Aaron and his sons to light a sleeping lamp from the afternoon until the morning before the Lord with what is prescribed by the law and is eternal in all your generations.
The custom of placing candles in tombs and houses is an act of piety of Christians that pleases God and the Saints and together soothes the souls of the dead.
Regarding the lighting of candles in the graves of the fallen, Saint Nicodemus of Mount Athos says that
Candles are lit for the forgiveness of the sins of those who offer it, as long as they are revived in God and in the Saints, so are the sins of those who are either alive or dead, as Martyr Demetrios said to the apostle
And Agios Kosmas the Aetolian advised
My brethren, do not grieve for those who are saved, but if you love your loved ones, do what you can for the soul of the forty-year-old, memorials, services, candle, frankincense, oil, fasting, prayers, alms.
God takes his mercy and saves your savior and takes him to Paradise or his hell is lighter. And as many women as you wear dirty for your sake, take them out, because you are hurting your speech, you are hurting your savages as well.