There is a sense of breaking life down. A person's inclination to give to society needs to be analyzed in a vacuum. We can talk about whether the Christmas story is true completely separately from why people get caught up in the Christmas spirit. We can promote a sexual morality that completely ignores the dignity of the human person and then wonder why people don't sacrifice for their fellow man like they used to. The reality is that serving God and serving family are the strongest motivators for doing good. Yet we work so hard to undermine both and then are shocked when people are less concerned with the good of society.
What is our connection with eternity? There is life after death and there are the children we raise. A person who is godless and sterile is never going to think about eternity. In fact, they don't even want to think about growing old. So why would it matter if they leave the world a better place then they found it? It is a nice sentiment but how much short term self-interest are you willing to give up for such nice sentiments? When it comes down to giving time and money we it doesn't happen.
The truth is it is easy for Christians to get caught up in the same thinking. We talk about storing up treasures in heaven but do we do it? We also talk about having love relationships that last and bear much fruit. Yes that means children but that is just part of it. True agape love will always overflow and bless others. But how often do we sterilize relationships? To make relationships fun but not fruitful. People can enjoy listening to the word of God for many years and not really change their lives. We need to have an openness to life that permeates everything we do. It starts with out sexuality because that is an icon for our entire spiritual life. But it has to go beyond that. We need to avoid the superficial pleasures and desire the deep joy that comes form lasting fruit.
For all the analysis of how we arrived at such a faithless society and even such a faithless church there is not a lot of mystery about how to fix it. We need saints. People who decide to embrace the faith fully and love sacrificially and intercede for lost souls. Mat 13:23 says:
But the seed falling on good soil refers to someone who hears the word and understands it. This is the one who produces a crop, yielding a hundred, sixty or thirty times what was sown.We need to be one of those seeds. That does not means we need to have that many biological children. But we should have that many spiritual children. We need to be open to God's seed. To nurture them into fruit that will last.