The natural Purpose of life is Sustainable survival
Many people have various goals in life that they call “purpose”, but purpose is higher level than goals. Goals stem from a purpose. Most religions propose or even instill some purpose of life, but such purpose is based on belief and therefore cannot be justified by facts and logic.
The natural rational purpose of life of any living organism including human is sustainable survival and humans are no different. Survival has three horizons. In the short horizon, instinct guide our own survival. In the mid-horizon, we have children to ensure survival of our genes and memes. And in long-horizon, we need to ensure our next generations can survive. Long survival horizon requires long-term priorities which conflict with our incentives and therefore is the most endangered.
We seek happiness on top of survival, yet there is no happiness without survival.