But although our intellect moves itself to some things, yet others are supplied by nature, as are first principles, which it cannot doubt; and the last end, which it cannot but will. Hence, although with respect to some things it moves itself, yet with regard to other things it must be moved by another. Wherefore that being whose act of understanding is its very nature, and which, in what it naturally possesses, is not determined by another, must have life in the most perfect degree. Such is God; and hence in Him principally is life. From this the Philosopher concludes (Metaph. xii, 51), after showing God to be intelligent, that God has life most perfect and eternal, since His intellect is most perfect and always in act.
Reply Obj. 1: As stated in Metaph. ix, 16, action is twofold. Actions of one kind pass out to external matter, as to heat or to cut; whilst actions of the other kind remain in the agent, as to understand, to sense and to will. The difference between them is this, that the former action is the perfection not of the agent that moves, but of the thing moved; whereas the latter action is the perfection of the agent. Hence, because movement is an act of the thing in movement, the latter action, in so far as it is the act of the operator, is called its movement, by this similitude, that as movement is an act of the thing moved, so an act of this kind is the act of the agent, although movement is an act of the imperfect, that is, of what is in potentiality; while this kind of act is an act of the perfect, that is to say, of what is in act as stated in De Anima iii, 28. In the sense, therefore, in which understanding is movement, that which understands itself is said to move itself. It is in this sense that Plato also taught that God moves Himself; not in the sense in which movement is an act of the imperfect.
Reply Obj. 2: As God is His own very existence and understanding, so is He His own life; and therefore He so lives that He has no principle of life.
Reply Obj. 3: Life in this lower world is bestowed on a corruptible nature, that needs generation to preserve the species, and nourishment to preserve the individual. For this reason life is not found here below apart from a vegetative soul: but this does not hold good with incorruptible natures. _______________________
FOURTH ARTICLE [I, Q. 18, Art. 4]
Whether All Things Are Life in God?
Objection 1: It seems that not all things are life in God. For it is said (Acts 17:28), "In Him we live, and move, and be." But not all things in God are movement. Therefore not all things are life in Him.
Obj. 2: Further, all things are in God as their first model. But things modelled ought to conform to the model. Since, then, not all things have life in themselves, it seems that not all things are life in God.
Obj. 3: Further, as Augustine says (De Vera Relig. 29), a living substance is better than a substance that does not live. If, therefore, things which in themselves have not life, are life in God, it seems that things exist more truly in God than themselves. But this appears to be false; since in themselves they exist actually, but in God potentially.
Obj. 4: Further, just as good things and things made in time are known by God, so are bad things, and things that God can make, but that never will be made. If, therefore, all things are life in God, inasmuch as known by Him, it seems that even bad things and things that will never be made are life in God, as known by Him, and this appears inadmissible.