Why does everything serve to humanity?

Just as, a trees serving to the fruit with its entire root, body, branches and leaves, this realm of existence serves to humanity. It is the recognition of the grace of God towards humans. This meaning is hidden in, Gods appointment of humankind as the caliphs on earth.

It is stated as, world is the field of the hereafter in a Hadith. The most important crop of the field of world is human. In addition, both heaven and hell as gathering centers of the realm of hereafter were prepared for humans. As heaven and hell are for humans, every creature is created for the benefit of humans, they are responsible for serving humanity, working for humanity, or rather a Divine Mercy and Wisdom makes them serve to humanity.