What do these passages say is the primary purpose of human life, and how should we use our time on Earth?

The primary purpose of life is not earning money but earning the knowledge of Truth, which is the non-dual knowledge of the Supreme Self. As explained in Chapter 8, the ultimate goal of human birth is to realize this truth and achieve satisfaction in one's own nature. The human body is presented as a unique and invaluable means to achieve this and the other four goals of life (purusharthas). Therefore, the text strongly advises that one should strive for Self-knowledge before the body falls, making sure not to ignore even a single moment of this precious opportunity.