Like middle-class society itself, what a Defoe novel shows, and what it says, move at quite different levels. There is a blank at the heart of these works, where a relation between God and your bank balance, prayer and the purchase of slaves, ought to be. This is because a form of society is emerging in England which is moving beyond the religious and metaphysical in practice, but which still needs to appeal to such principles in theory. Unless it did, it would be hard put to justify its existence. In practice, the world is just one random material situation after another, without overall point or pattern. In theory, it all adds up to some beneficent Providence. In theory, things have God-given values; in practice, their value lies in what you can get for them on the market. In theory, moral values are absolute; in practice, nothing in this mobile, ceaselessly mutating society is absolute at all. The family, for a devout puritan like Defoe, is a sacred domain, as his work The Family Instructor suggests; it is just that ties of kinship are to be severed when they get in the way of your material advancement, as happens often enough in the novels. Family relations are sacrosanct bonds of blood; it is just that in practice they are to be broken, ignored or treated as purely instrumental.
– The English Novel