Marsilio Ficino’s Platonic Theology, Volume II

21Come, gather the whole fiery form, which in your three-cubit body is three cubits, into the center of the heart. From there let it grow as much in power as it has grown in unity, just as the sun's rays, gathered at the center of a concave bronze mirror, are strengthened so greatly that, rebounding from it, they suddenly set fire to and consume even the hardest things. Remove that small portion of the heart by which the form of fire is weighed down. Let an indivisible form remain—active, warm, and shining, and so in a different and more wonderful manner than before. Because it is indivisible and active throughout its whole self, let it illumine the whole body equally. Because it burns beyond belief, let it be alive and life-giving. Because it shines marvelously, let it sense. Let it also understand, if it is turned back upon itself and raised upward.

22Thus far, advancing step by step through things that can be touched, you have found the soul by proceeding from solid body to something like a point entirely free. Search for the soul again through things seen by the eyes. Why, I ask, do you distrust the existence of something spiritual in nature, when even with your eyes you see spirit in a certain fashion? You know that this light of the sun, manifest to the eye, is not body, because in an instant it pours itself into all things; once poured in, it neither shatters bodies nor is stained. Behold, you see spirit. Why do you deny it? Or perhaps you will deny the existence of whatever you do not see. If so, you will say that the spheres of air, fire, and heaven, more excellent than water and earth, are nothing because they are not visible. Thus the greatest and most excellent part of the world will be nothing because it cannot be seen. But let us return to light.