Objection 1. It would seem that man can be made happy through the action of some higher creature, viz. an angel. For since we observe a twofold order in things--one, of the parts of the universe to one another, the other, of the whole universe to a good which is outside the universe; the former order is ordained to the second as to its end (Metaph. xii, 10). Thus the mutual order of the parts of an army is dependent on the order of the parts of an army is dependent on the order of the whole army to the general. But the mutual order of the parts of the universe consists in the higher creatures acting on the lower, as stated in the I, 109, 02: while happiness consists in the order of man to a good which is outside the universe, i.e. God. Therefore man is made happy, through a higher creature, viz. an angel, acting on him.
Objection 2. Further, that which is such in potentiality, can be reduced to act, by that which is such actually: thus what is potentially hot, is made actually hot, by something that is actually hot. But man is potentially happy. Therefore he can be made actually happy by an angel who is actually happy.
Objection 3. Further, Happiness consists in an operation of the intellect as stated above (Question 3, Article 4). But an angel can enlighten man's intellect as shown in the I, 111, 1. Therefore an angel can make a man happy.
On the contrary, It is written (Psalm 83:12): "The Lord will give grace and glory."
I answer that, Since every creature is subject to the laws of nature, from the very fact that its power and action are limited: that which surpasses created nature, cannot be done by the power of any creature. Consequently if anything need to be done that is above nature, it is done by God immediately; such as raising the dead to life, restoring sight to the blind, and such like. Now it has been shown above (Article 5) that Happiness is a good surpassing created nature. Therefore it is impossible that it be bestowed through the action of any creature: but by God alone is man made happy, if we speak of perfect Happiness. If, however, we speak of imperfect happiness, the same is to be said of it as of the virtue, in whose act it consists.
Reply to Objection 1. It often happens in the case of active powers ordained to one another, that it belongs to the highest power to reach the last end, while the lower powers contribute to the attainment of that last end, by causing a disposition thereto: thus to the art of sailing, which commands the art of shipbuilding, it belongs to use a ship for the end for which it was made. Thus, too, in the order of the universe, man is indeed helped by the angels in the attainment of his last end, in respect of certain preliminary dispositions thereto: whereas he attains the last end itself through the First Agent, which is God.
Reply to Objection 2. When a form exists perfectly and naturally in something, it can be the principle of action on something else: for instance a hot thing heats through heat. But if a form exist in something imperfectly, and not naturally, it cannot be the principle whereby it is communicated to something else: thus the "intention" of color which is in the pupil, cannot make a thing white; nor indeed can everything enlightened or heated give heat or light to something else; for if they could, enlightening and heating would go on to infinity. But the light of glory, whereby God is seen, is in God perfectly and naturally; whereas in any creature, it is imperfectly and by likeness or participation. Consequently no creature can communicate its Happiness to another.
Reply to Objection 3. A happy angel enlightens the intellect of a man or of a lower angel, as to certain notions of the Divine works: but not as to the vision of the Divine Essence, as was stated in the I, 106, 1: since in order to see this, all are immediately enlightened by God.
Source: Summa Theologica (New Advent)