Why is this the answer?

The answer is fur because this riddle tells a clever and tricky story about the beautiful, warm coat that belongs to many animals. It uses several clues to describe fur's whole life journey, from keeping an animal safe to being used by people later on. Let us look closely at the first two lines, which hold the most interesting secret: "My first master has four legs, my second master has two. My first I serve in life, my second I serve in death." The "first master with four legs" is the animal itself, like a fox, a rabbit, or a beaver, who is alive and running around. Fur is one of the most important parts of an animal's body because it works like a super warm blanket, keeping them snug and dry, especially when it is cold or snowing outside. The fur is serving the animal by protecting it and helping it survive. The "second master with two legs" is a human being. Sometimes, after an animal passes away, its soft, durable fur is used by people to make warm clothes like jackets, hats, or scarves. Because the fur is no longer attached to the living animal, the riddle says it is serving the human in death by keeping them warm. The next clue is about how the fur feels when you touch it: "Tough I am, yet soft beside." This is a way of saying that even though fur is very pleasant and nice to cuddle up with, it is also very strong. The individual hairs are durable and can hold up against snow and wind, allowing the finished product to last a long time. It is tough enough to be used outside, but soft enough to feel good against your skin. Finally, the riddle gives a very specific picture clue: "Against ladies cheeks I often reside." If you have ever seen a warm, hooded winter coat, you know that sometimes the edge of the hood is trimmed with a strip of soft, fluffy fur. This trim is often placed right where the coat touches the person's face and neck. The soft fur rests right against the cheek of the person wearing the coat, keeping them extra warm and cozy in the freezing weather, just as the riddle describes. These clues all fit perfectly together to tell the story of fur.