Again, natural joy, arising from natural principles, and unchecked and unregulated by gracious influences, has oftentimes a very powerful effect upon the physical system. And it is possible and even probable, that this may sometimes be the case with true spiritual or gracious joy; especially when the emotion is strong and immediately successive to a painfully depressed and suffering state of mind. And it is not unreasonable to suppose, that, in some cases, when powerful physical results are found to exist, that there may be a union or combination of natural and gracious emotion. But it is nevertheless true, that the natural tendency of spiritual joy, IN ITSELF CONSIDERED, and independently of any peculiar circumstances, is, in a remarkable degree, and much more so than that of mere natural joy, to produce a tranquilizing effect upon the mind and through the mind upon the physical system, and to promote soundness and regularity of action in both.
— The Interior or Hidden Life (1844) Part 1, Chapter 15.