Everything is Nature is there for a purpose; i.e. pigeons, ants, rats. They all have a purpose. Theirs is to clean up the environment. They are the cleaners. I have yet to find a purpose for Mosquitos but then .... maybe their purpose is to spread disease to check otherwise uncontrollable populations.
Everything in Nature has a purpose. Every Human being has a purpose. First, it is "to be". To have being. To have being is Good. How can we have spiritual immortality if we don't have physical existence first? That is kind of hard isn't?
My big toe doesn't say, "I am not the Brain or the Heart or the eye so I am just going to off meself". The body needs the big toe. Everything we have we need; even the tiniest insequential part. One can say that One blood cell is unimportant but if all the cells thought so, then where would we be--dead.
Life is hard. That is a famous ancient Greek saying--"The good comes through the Hard". The Hard life makes us better. The law of Thermodynamics is just as valid in the human sphere as it is in the physical realm. Only by putting "energy" in does the world turn, once energy stops, then entropy sets in.
Us, humans are both physical and spiritual. It is the higher ideals that give us meaning and it takes struggle to reach the higher ideals. The True, The Good and the Beautiful.