Take two glasses, in one is water, in the other none. The glass with water should be only half-full. Suppose you observe these two glasses in the external world. Now if you pour some of the water from the half-filled into the empty glass, the latter will be partly filled, while the other then has less water in it. If a second time you pour water from the glass which was half-filled into the glass which was at first empty, the first glass will have still less water in it; in short, through the pouring-out there is always less and less water in the glass which was at first half-full of water. That is a true presentation as regards the external physical sense-world.

Now let us form a different conception. By way of experiment, let us form the contrary idea. Imagine yourself again pouring water from the half-filled glass into the empty one. Into this latter there comes water, but you must imagine that in the half-filled glass by means of this pouring out of water there is more instead of less, and that if you poured from it a second time, so that again something passed  over into the previously empty glass, there would again be more and not less water left in the glass that was at first half-filled. As a result of the out-pouring, more and more water would be in the first glass. Imagine yourself picturing this idea. Of course everyone who at our present time counts himself among the thoroughly intelligent would say: “Why are you picturing an absolute delusion! You imagine that you are pouring out water, and that by so doing more water comes into the glass from which you are pouring!”

Of course if one applies this idea to the physical world, then, naturally, it is an absurd idea; but — marvelous to relate — it can be applied to the spiritual world. It can be applied in a singular manner. Suppose a man has a loving heart, and out of this loving heart he performs a loving action to another who needs love. He gives something to that other person; but he does not on that account become emptier when he performs loving actions to another; he receives more, he becomes fuller, he has still more, and if he performs the loving action a second time he will again receive more.

One does not become poor, nor empty, by giving love or doing loving actions, on the contrary, one becomes richer, one becomes fuller. One pours forth something into the other person, something which makes fuller oneself. Now, if we apply our picture (which is impossible, absurd, for the ordinary physical world), if we apply our picture of the two glasses to the outpouring of love, it becomes applicable; we can then grasp it as an image, as a symbol of spiritual facts.

Love is so complex a thing that no man should have the arrogance to attempt to define it, to fathom the nature of love. Love is complex; we perceive it, but no definition can express it.

– Rudolf Steiner, The Spiritual Beings in the Heavenly Bodies and in the Kingdoms Of Nature, Lecture 3