A candle relights when a match is held above the wick because its trail of smoke still contains some of the wax. When candles are burned, the heat of the flame turns the the wax (which is originally solid) into liquid (commonly near the wick) and then evaporates as gas. The vaporized wax actually protect the wick and this is the reason why it is not burned. So, when you put off a candle, the vaporized wax is still present near the wick. This, remember, holds heat and light energy. Thus, this explains why the candle can be relighted once you hold a match above the wick. It then allows the match to ignite.
