Theophylact of Ohrid — as excerpted in the Catena Aurea on Mark 12:28-34

“See how He has enumerated all the powers of the soul; for there is a 1living power in the soul, which He explains, when He says, With all thy soul, and to this belong anger and desire, all of which He will have us give to Divine love. There is also another power, which is called natural, to which belong nutriment and growth, and this also is all to be given to God, for which reason He says, With all thy heart. There is also another power, the rational, which He calls the mind, and that too is to be given whole to God.”