Mary Eberstadt of the Hoover Institution advances an interersting thesis in an article in Policy Review.
Most people, she says, assume that religion induces people to have bigger families. Eberstadt believes this gets it backward:
People who have larger families tend to be more religious. In Europe the decline in religiosity began after the decline in family size. In America where families still tend on average to be larger than their European counterparts religion is still relatively popular, though family size and religious popularity are both in decline.
To begin sketching an explanation of religious belief complementary to this one, one must answer this question: What could it be about the experience of the natural family that might make an individual more disposed toward religion than he is without it? Though merely a preliminary attempt at an answer, several lines of explanation suggest themselves.
You can read her reasoning at the link.
Oddly, Eberstadt omits perhaps the biggest reason why family-oriented people are more committed to church. This is the recognition by parents that children need all the moral instruction they can get and they're not likely to get it in any other institution in our society. If religion or the church should ever die it won't be too many generations afterward that the family will die as well.
Eberstadt makes a very good point when she notes that women are usually more invested in family than men and are also usually more invested in church than men. Churches are like a glue that helps hold families together. When churches are vibrant and strong the families which attend them are generally stronger. Women, on balance, are more conscious of their family's welfare and are much more likely to turn to the church for the help it can give.
Take away religion, as the secularist urges, and human beings soon come to see themselves as nothing more than autonomous random particles bouncing aimlessly through their meaningless lives until death puts an end to their empty, absurd existence. There's not much point to the commitments and sacrifices required to sustain a family in the cold, sterile world the secularist would create for us.
RLC