That's a great question!
Warming up before singing is important for several reasons. Changing one's pitch during warm up allows the muscles involved in signing to stretch, including the diaphragm and muscles in the torso to stretch, which will influence the sound of the voice. Warming up also allows the singer to practice vocalization exercises, including control of breath, diction (sounding of the words), and how the sound is blended. Other factors that influence a person's vocal range, which is a measure of the range of pitches a person can make, include the folds of their larynx and the shape and size of the vocal tract. These are features that are biological, but singers can learn techniques to improve their resonance within their vocal tract by projecting sounds in certain ways, a technique known as vocal resonation.