Does a bird serve its purpose when it sings or when it sits on eggs? Perhaps when it lays the eggs if the bird is a chicken and you like eggs for breakfast, but I digress.

The point is that you serve purpose when you exist and share, when you love and care, and when you work, and when you are fair.

Being is its own purpose and by design of those greater than us. You can find comfort within your own mind with that if you allow yourself.