Pesachim 8 - The light of a candle
We mentioned before that one should search for chametz using the light of a candle. Why a candle? It comes through a chain of associations. Chametz should "not be found." This leads to remember Joseph who "searched and found" (a divining goblet in the sack of Benjamin). The "found" leads to the words of the prophet who promises that God will look for the errors of the people of the city of Jerusalem using the light of candles, and not "find" any. And finally "candles" leads to the words of king Solomon that "The soul of a man is the candle of God, which God uses to inspect the deeds of man."
Why do we need the last connection, from "candles" to "candle?" It is already pretty clear and close by then! - Because one might think that searching with candles is a leniency, and God will overlook some errors precisely because of using candles. To show that this is untrue, we bring the last proof of candle being the light of God.
Still, why not use a torch? First, because with the torch he will be afraid to examine nooks and crevices, since he may cause fire. Also, a torch gives unsteady flame, while that of a candle is constant. Yet another reason is that one carries a torch behind himself, and the candle he carries in front.
Art: Boy with a Torch by Matthias Stomer (1600 - 1650)