"How the light of reason is necessary to every soul that wishes to serve God in truth" - part I - "THE DIALOGUE" OF SAINT CATHERINE OF SIENA - Translated by Algar Thorold; #26
The first light:
"...concerning the three lights which issue from Me, the True Light. The first is a general light dwelling in those who live in ordinary charity... The other two lights dwell in those who, having abandoned the world, desire perfection...
The first lightens you all to know the transitory nature of the things of the world, all of which pass like the wind. But this you cannot know thoroughly, unless you first recognize your own fragility, how strong is your inclination, through the law of perversity with which your members are bound, to rebel against Me, your Creator (not that by this law any man can be constrained to commit any, even the smallest sin, against his will, but that this law of perversity fights lustily against the spirit). I did not impose this law upon you, in order that My rational creature should be conquered by it, but in order that he should prove and increase the virtue of his soul, because virtue cannot be proved, except by its contrary.
Sensuality is contrary to the spirit, and yet, by means of sensuality, the soul is able to prove the love which she has for Me, her Creator. How does she prove it? When, with anger and displeasure, she rises against herself. This law has also been imposed in order to preserve the soul in true humility.
Wherefore you see that, while I created the soul to Mine own image and similitude, placing her in such dignity and beauty, I caused her to be accompanied by the vilest of all things, imposing on her the law of perversity, imprisoning her in a body, formed of the vilest substance of the earth, so that, seeing in what her true beauty consisted, she should not raise her head in pride against Me. Wherefore, to one who possesses this light, the fragility of his body is a cause of humiliation to the soul, and is in no way matter for pride, but rather for true and perfect humility.
"And similarly if the soul know not good, and the reason of good, that is to say virtue, she cannot love or desire either Me, who am the Essential Good, or virtue, which I have given you as an instrument and means for you to receive My grace, and Myself the True Good. See then how necessary is this light, for your sins consist in nothing else than in loving that which I hate, and in hating that which I love. I love virtue and hate vice; he who loves vice and hates virtue offends Me, and is deprived of My grace. Such a one walks as if blind, for he knows not the cause of vice, that is, his sensual self-love, nor does he hate himself on account of it; he is ignorant of vice and of the evil which follows it: he is ignorant of virtue and of Me, who am the cause of his obtaining life-giving virtue; he is ignorant of his own dignity, which he should maintain by advancing to grace, by means of virtue. See, therefore, how his ignorance is the cause of all his evil, and how you also need this light, as has been said."