Because
then, people will hate and kill their own brothers / sisters for the chance to be
rewarded in the afterlife; while their religious leaders (politicians) are
rewarded with
earthly treasures (money and power) No religious sect in the world today is unimpeachable.
Scipio turns his eyes back to the earth, and Africanus exhorts him to see how insignificant worldly glory is in comparison to the celestial realms, or even to the vast uninhabitable regions of the globe, or to the unimaginable immensity of the Great Year of the cosmic aeon, and
then tells him to fix his mind always on heavenly things, to ignore
earthly rewards and
earthly censure alike, and to be guided only by virtue.