The sublime, yet never wholly attainable, idea of an ethical commonwealth dwindles markedly under men’s hands. It becomes an institution which, at best capable of representing only the pure form of such a commonwealth, is, by the conditions of sensuous human nature, greatly circumscribed in its means for establishing such a whole. How indeed can one expect something perfectly straight to be framed out of such crooked wood?
To found a moral people of God is therefore a task whose consummation can be looked for not from men but only from God Himself. Yet man is not entitled on this account to be idle in this business and to let Providence rule, as though each could apply himself exclusively to his own private moral affairs and relinquish to a higher wisdom all the affairs of the human race (as regards its moral destiny). Rather must man proceed as though everything depended upon him; only on this condition dare he hope that higher wisdom will grant the completion of his well-intentioned endeavors.
The wish of all well-disposed people is, therefore, “that the kingdom of God come, that His will be done on earth.” But what preparations must they now make that it shall come to pass? An ethical commonwealth under divine moral legislation is a church which, so far as it is not an object of possible experience, is called the church invisible (a mere idea of the union of all the righteous under direct and moral divine world-government, and idea serving all as the archetype of what is to be established by men. The visible church is the actual union of men into a whole which harmonizes with that ideal.
Immanuel Kant, Religion within the Bounds of Reason Alone. A very Lutheran way of putting it; there's a reason why someone as very different from Kant as Karl Barth insisted that Kant had a good grasp of the Protestantism of the Reformation. But the point it makes is more general than that.
