The great power and characteristic of light is, that it refuses the entrance of darkness on every side of it. Be it ever so small a light, there is no access to it on any side. It is isolated to everything but itself, though with itself it will so unite that you could not distinguish in the unity between the light furnished by the largest lamp and the smallest rushlight.
It is exclusive; i.e. it will not admit of any admixture; but the more it is increased, the more it will assert its isolation; though, at the same time, with each increase will it offer and present a benefit to any one in need of it, so that when most distinct, it is morally best qualified to offer and bestow, in a delicate, unobtrusive way, the most valued services. In Romans 13:12 we are told to "put on the armour of light;" in the original, the "arms of light;" i.e. the weapons - the powers of defence as well as attack. Light becomes not only a panoply, but a weapon; for "light is that which doth make manifest;" necessarily painful to that which is manifested and exposed, but preservative to that for which it acts.
Refusing all intermixture or association with anything but itself, it will nevertheless co-operate and coalesce with the smallest fraction of light, which only renders it stronger in its own intrinsic qualities. If I walk in light, I am unconsciously helping the smallest ray of it in my associates. Whatever be the measure of it in me or in them, the two coming in contact must necessarily blend, and act in delicate and conjoint co-operation. So that there is a mutual benefit, often unknown or undefined, save in the sense of being preserved from the works of darkness. Nature is rebuked, but so rebuked on all sides that it is more subdued and less irritated than if, as in a guerilla warfare, it were attacked, now in one place, and now in another. Often when we are trying to behave well in given circumstances, and are making arrangements how we shall act, we shall find how vain our plans have been. Nature, though irritated, is not subdued by our forecasting; whereas if we walk in the least measure of light known to us, we shall most effectually preserve ourselves, as well as offer, and (if acceptable) bestow the best service to our surroundings. The higher we get, the more do we feel encompassed, and possessed of the "arms of light;" and the more we know what light is, the more truly shall we estimate all that is opposed to it.