The "true" meaning of something is attached by the human beings who deal with that thing.
Mountains have no meaning "in themselves" but become beauty for the observer, fun for me on the switchbacks, a mortal challenge for the climber.
The curse of naming things
The Western human curse is having to name things — to give them meaning. The side effect is our opportunistic and instrumental view of the world and other animals — which is leading us to ecological Apocalypse and the end of our species. The positive effect is the tabula rasa: no meaning is given transcendently. It must be built and negotiated with the world.
I don't see why our own life should be the exception to this universal cultural and cognitive rule. Exceptions are always ugly in the search for truth.
The purpose is to search for purpose
Therefore the purpose of life is exactly what we'd expect: to search for a purpose in life.
And just as the mountain's purpose for humans isn't to aggregate rocks but goes beyond, referring to those who observe and rejoice, so the purpose of our life should refer to the world and to others. Otherwise it would be a self-referential life.
Self-referential lives are useless
And self-referential lives — based on selfishness, basic urges, money, power, consumption, resource waste, lack of critical thinking, values, and willingness to improve the world — are, simply, useless.
This doesn't mean we should kill all the petite bourgeoisie, but that if you choose a B-grade life, you're throwing it away.
If we had been born in the East or in different cultures, we would have different problems. In this answer I speak of us Westerners in our DNA and our original cultural formatting that isn't really modifiable.
