Moreover, revelation considered only as subservient to natural religion, is important as an external institution of it. As miraculous powers were given to the first preachers of Christianity, in order to their introducing it into the world, a visible church was established, in order to continue it, and carry it on successively throughout all ages. This visible church is like a city built upon a hill, a standing memorial to the world of the duty which we owe our Maker—a repository of the oracles of God. It prevents us forgetting the reality of religion, by the form of it being ever before our eyes; and it has a further tendency to promote natural religion, as being an instituted method of education, that the body of Christ, as the Scripture speaks, should be edified. The benefit of a visible church being thus apparent, it follows that positive institutions are beneficial, for the visibility of the church consists in them.
Butler, Analogy of Religion, Part 2, Chapter 1. [ADDED LATER -- I wasn't quite thinking when I put this reference; this is actually Hobart's summary of Butler, not Butler himself, although Hobart sticks fairly close to Butler's argument. Butler's argument in his own words can be found here.] Of course, Butler doesn't think we should consider revelation "only as subservient to natural religion", only that a visible system of religious institutions does in fact increase our ability to participate even in natural religion in a manner appropriate to it. A similar point can be made about the 'spiritual but not religious' type of our days; namely, that if that were really your goal, actually participating in religious institutions would further it, just as a matter of human nature.