A justly famous paragraph:
It is indeed sometimes said that the stream is clearest near the spring. Whatever use may fairly be made of this image, it does not apply to the history of a philosophy or belief, which on the contrary is more equable, and purer, and stronger, when its bed has become deep, and broad, and full. It necessarily rises out of an existing state of things, and for a time savours of the soil…In time it enters upon strange territory; points of controversy alter their bearing; parties rise and around it; dangers and hopes appear in new relations; and old principles reappear under new forms. It changes with them in order to remain the same. In a higher world it is otherwise, but here below to live is to change, and to be perfect is to have changed often (Newman, Development, 1.1.7).
Chesterton glosses this idea still more memorably: “all conservatism is based upon the idea that if you leave things alone you leave them as they are. But you do not. If you leave a thing alone you leave it to a torrent of change. If you leave a white post alone it will soon be a black post. If you particularly want it to be white you must be always painting it again; that is, you must be always having a revolution. Briefly, if you want the old white post you must have a new white post” (Orthodoxy, Ch. 1).