What is C.S. Lewis saying about the human condition in society in Out of the Silent planet?

This story is primarily a Christian allegory. Lewis is pointing out that man on Earth is fallen. Man (people) have been seduced by dark forces to turn away from the light of God and seek meaning in greed and endless desire. The human condition must turn away from material delights towards a higher benevolent power if it is ever to free itself from sin and temptation.