10. If one studies all the passions, and even all vices, one sees that they have their origin in the instinct of self-preservation. This instinct is strongest with animals, and with primitive men, who approached nearest the animal existence. It governed them entirely, because they had not the moral sense for a counterpoise, having not been born into the intellectual life. The instinct is weakened in proportion as intelligence is developed, because the latter rules matter.
The spirit is destined for the spiritual life: but in the first phases of its corporeal existence it has only material needs to satisfy; and to this end the exercise of the passions is a necessity for the preservation of the species and of the individual, materially speaking. But, passed beyond this period, he has other needs, - needs at first partly moral and partly material, then exclusively moral. It is then that the spirit rules matter. If he throws of the yoke, he advances on his providential way; he approaches his final destiny. If on the contrary, he allows himself to be ruled by the senses, he is held back on his upward progress by assimilating himself with the brute. In this situation that which was formerly good, because it was a necessity of his nature, becomes an evil, not only because it is no more a necessity, but because it has become hurtful to his spiritual well-being. Similarly, that which is considered a good quality in a child becomes an imperfection in the adult. Evil is thus relative, and the responsibility therefore proportionate to the degree of advancement.
All passions have thus their providential utility; if not so, God has made some things intrinsically useless and hurtful. It is only abuse which constitutes the evil, and man abuses by virtue of his free-will. At length, awakened to the knowledge of his own share in it, he chooses freely between the good and the bad.