The human soul consists of three principal faculties, vegetative, animal, rational. Corresponding to these the principal virtues and vices are also three. The vegetative power, whose functions are nourishment, growth and reproduction, is related to appetite, and is called the appetitive soul. The animal power as being the cause of sensation, voluntary motion, cruelty, revenge, mercy and kindness, is called the spirited soul, because these qualities are dependent upon the energy or weakness of the spirit. The rational power has two aspects. One is directed upwards and is the means of our learning the sciences and the arts. The other aspect is directed downwards, and endeavors to control (successfully or not as the case may be), the two lower powers of the soul, guarding them against excess and defect. This function we call conduct, and virtue is the mean between the two extremes of too much and too little. The mean of the appetitive power is temperance; of the spirited power, bravery and gentleness; of the rational soul, justice.[245] Justice consists in giving everything its due without excess or defect. Justice is therefore the highest of all qualities, and is of value not merely in a person's relations to his family and country, but also in the relations of his powers one to another. The rational power must see to it that the two lower faculties of the soul get what is their due, no more and no less. This quality has an important application also in the relations of a man to his maker. It is just that a person should requite his benefactor as much as he received from him, if possible. If he cannot do this, he should at least thank him. Hence the reason for divine worship, the first of commandments. This quality, the greatest of men possessed in the highest degree. Moses "said to him that did the wrong, wherefore smitest thou thy fellow?" (Ex. 2, 13). And when the shepherds came and drove away the daughters of the priest of Midian, "Moses stood up and helped them, and watered their flock" (_ib._ 17). This is the reason why God sent him to deliver Israel.