Why is this the answer?

The answer is candle because this clever riddle uses fun word pictures to describe a simple object that helps light up the dark when we need it most. To solve the puzzle, we can be detectives and look at each clue one by one to see how they fit. The first clue is, "My life can be measured in hours." When you light a candle, it starts to burn. It does not live like a person or a pet, but its time is measured by how long the wax lasts. A new candle can burn for a long time, maybe for a few hours, before it is completely gone. That time is its life. Next, the riddle says, "I serve by being devoured." This is a clever way of saying that the candle helps us by being slowly eaten up by the flame. The fire uses the wax as food, or fuel, which is why a candle gets shorter as it burns. Its whole job is to be consumed to give us light. The riddle then gives us clues about size and speed: "Thin, I am quick. Fat, I am slow." This is a perfect way to describe the different types of candles you might see. Think about a tiny, skinny birthday candle; you light it, sing the song, and it burns up quickly, which is why it is "quick." Now think about a large, wide candle, like a big pillar candle. Because it has much more wax, it takes many, many hours for the fire to use it all up, making it burn "slow." The more wax a candle has, the longer its life will be. The final clue is, "Wind is my foe." A foe is another word for an enemy. This is the easiest clue to figure out because everyone knows that a sudden puff of wind, or even a deep breath, can instantly put out a candle's flame. The wind is the candle's biggest enemy because it stops the light from shining. All of these clever clues point right to the candle.