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.
Objection 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.
Objection 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.
Objection 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 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.
On the contrary, (John 1:3-4), it is said, "What was made, in Him was life." But all things were made, except God. Therefore all things are life in God.
I answer that, In God to live is to understand, as before stated (3). In God intellect, the thing understood, and the act of understanding, are one and the same. Hence whatever is in God as understood is the very living or life of God. Now, wherefore, since all things that have been made by God are in Him as things understood, it follows that all things in Him are the divine life itself.
Reply to Objection 1. Creatures are said to be in God in a twofold sense. In one way, so far are they are held together and preserved by the divine power; even as we say that things that are in our power are in us. And creatures are thus said to be in God, even as they exist in their own natures. In this sense we must understand the words of the Apostle when he says, "In Him we live, move, and be"; since our being, living, and moving are themselves caused by God. In another sense things are said to be in God, as in Him who knows them, in which sense they are in God through their proper ideas, which in God are not distinct from the divine essence. Hence things as they are in God are the divine essence. And since the divine essence is life and not movement, it follows that things existing in God in this manner are not movement, but life.
Reply to Objection 2. The thing modelled must be like the model according to the form, not the mode of being. For sometimes the form has being of another kind in the model from that which it has in the thing modelled. Thus the form of a house has in the mind of the architect immaterial and intelligible being; but in the house that exists outside his mind, material and sensible being. Hence the ideas of things, though not existing in themselves, are life in the divine mind, as having a divine existence in that mind.
Reply to Objection 3. If form only, and not matter, belonged to natural things, then in all respects natural things would exist more truly in the divine mind, by the ideas of them, than in themselves. For which reason, in fact, Plato held that the "separate" man was the true man; and that man as he exists in matter, is man only by participation. But since matter enters into the being of natural things, we must say that those things have simply being in the divine mind more truly than in themselves, because in that mind they have an uncreated being, but in themselves a created being: whereas this particular being, a man, or horse, for example, has this being more truly in its own nature than in the divine mind, because it belongs to human nature to be material, which, as existing in the divine mind, it is not. Even so a house has nobler being in the architect's mind than in matter; yet a material house is called a house more truly than the one which exists in the mind; since the former is actual, the latter only potential.
Reply to Objection 4. Although bad things are in God's knowledge, as being comprised under that knowledge, yet they are not in God as created by Him, or preserved by Him, or as having their type in Him. They are known by God through the types of good things. Hence it cannot be said that bad things are life in God. Those things that are not in time may be called life in God in so far as life means understanding only, and inasmuch as they are understood by God; but not in so far as life implies a principle of operation.
Source: Summa Theologica (New Advent)