Basically because its the basic building blocks of who we were. What living things are made up of. Every one of the four macromolecule having a spefice purpose, a very vital purpose on helping us live. For example, carbohydrates help us store are energy so when we are runing low we have more. We all need energy don't we. Also without proteins we wouldn't be strong or beable to fight off deseases. So we wouldn't be really living that long. So really all of the molecules are vital to the human body because its what we are made of. It's what makes us up.