In short, the enlightenment privatized marriage, taking it out of the public sphere, and redefined its purpose as individual gratification, not any 'broader good' such as reflecting God's nature, producing character, or raising children. Slowly but surely, this newer understanding of the meaning of marriage has displaced the older ones in Western culture.
Timothy KellerFaith in the gospel restructures our motivations, our self-understanding, our identity, and our view of the world. Behavioral compliance to rules without heart-change will be superficial and fleetingโฆ We can only change permanently as we take the gospel more deeply into our understanding and into our hearts. We must feed on the gospel, as it were, digesting it and making it part of ourselves. That is how we grow.
Timothy KellerThose who believe they have pleased God by the quality of their devotion and moral goodness naturally feel that they and their group deserve deference and power over others. The God of Jesus and the prophets, however, saves completely by grace. He cannot be manipulated by religious and moral performance--he can only be reached through repentance, through the giving up of power. If we are saved by sheer grace we can only become grateful, willing servants of God and of everyone around us.
Timothy KellerEveryone will be forgotten, nothing we do will make any difference, and all good endeavors, even the best, will come to naught. Unless there is God. If the God of the Bible exists, and there is a True Reality beneath and behind this one, and this life is not the only life, then every good endeavor, even the simplest ones, pursued in response to God's calling, can matter forever.
Timothy Keller