Candles in church

Answering questions depends on the personality of the questioner, the time of day, the quality of your friendship, and many other variables too subtle to think of in the abstract and in advance. A few rejoinders spring to mind:

"For the same reason we put candles on birthday cakes."

"Because there was a perpetual light kept burning in the Temple."

"Because it's fun. Candlelight is so cool!"

"We found that the candles generate lots of revenue for the Church." :D

"Why not?"

"Evolution gave us great joy in watching fires burn. Lighting a candle satisfies our Neanderthal DNA. It is a tiny bonfire. It is fun to watch things burn."

"Because it feels good."

"For the same reason concertgoers light matches at rock concerts, except for the alcohol, drugs, sex, and rock-'n'-roll."

"Because it is easier for me to burn a candle for a day than to pray continually for a day."

"Because my Mom did it."

"I don't know. Why do you ask?"

"Because it is something extra."

Oh, wait. I actually have an answer in my case. I decided years ago that I wanted to make the Easter season special. Lent works because our spiritual practices intrude on every meal we take and affect how we live each day. I wanted some kind of ritual that would be DIFFERENT from my ordinary days and that would remind me that I was in the Easter season, looking forward to Pentecost. So I gradually developed the habit of burning my own Easter candle in imitation of the Paschal candle that is lit at every Mass in the Easter season. I light the candle, say the Sequence for Pentecost, leave it burning until the right amount of wax has been consumed, then extinguish it.