Objection 1. It would seem that one angel can move another angel's will. Because, according to Dionysius quoted above (Article 1), as one angel enlightens another, so does he cleanse and perfect another. But cleansing and perfecting seem to belong to the will: for the former seems to point to the stain of sin which appertains to will; while to be perfected is to obtain an end, which is the object of the will. Therefore an angel can move another angel's will.
Objection 2. Further, as Dionysius says (Coel. Hier. vii): "The names of the angels designate their properties." Now the Seraphim are so called because they "kindle" or "give heat": and this is by love which belongs to the will. Therefore one angel moves another angel's will.
Objection 3. Further, the Philosopher says (De Anima iii, 11) that the higher appetite moves the lower. But as the intellect of the superior angel is higher, so also is his will. It seems, therefore, that the superior angel can change the will of another angel.
On the contrary, To him it belongs to change the will, to whom it belongs to bestow righteousness: for righteousness is the rightness of the will. But God alone bestows righteousness. Therefore one angel cannot change another angel's will.
I answer that, As was said above (Question 105, Article 4), the will is changed in two ways; on the part of the object, and on the part of the power. On the part of the object, both the good itself which is the object of the will, moves the will, as the appetible moves the appetite; and he who points out the object, as, for instance, one who proves something to be good. But as we have said above (Question 105, Article 4), other goods in a measure incline the will, yet nothing sufficiently moves the will save the universal good, and that is God. And this good He alone shows, that it may be seen by the blessed, Who, when Moses asked: "Show me Thy glory," answered: "I will show thee all good" (Exodus 33:18-19). Therefore an angel does not move the will sufficiently, either as the object or as showing the object. But he inclines the will as something lovable, and as manifesting some created good ordered to God's goodness. And thus he can incline the will to the love of the creature or of God, by way of persuasion.
But on the part of the power the will cannot be moved at all save by God. For the operation of the will is a certain inclination of the willer to the thing willed. And He alone can change this inclination, Who bestowed on the creature the power to will: just as that agent alone can change the natural inclination, which can give the power to which follows that natural inclination. Now God alone gave to the creature the power to will, because He alone is the author of the intellectual nature. Therefore an angel cannot move another angel's will.
Reply to Objection 1. Cleansing and perfecting are to be understood according to the mode of enlightenment. And since God enlightens by changing the intellect and will, He cleanses by removing defects of intellect and will, and perfects unto the end of the intellect and will. But the enlightenment caused by an angel concerns the intellect, as explained above (Article 1); therefore an angel is to be understood as cleansing from the defect of nescience in the intellect; and as perfecting unto the consummae end of the intellect, and this is the knowledge of truth. Thus Dionysius says (Eccl. Hier. vi): that "in the heavenly hierarchy the chastening of the inferior essence is an enlightening of things unknown, that leads them to more perfect knowledge." For instance, we might say that corporeal sight is cleansed by the removal of darkness; enlightened by the diffusion of light; and perfected by being brought to the perception of the colored object.
Reply to Objection 2. One angel can induce another to love God by persuasion as explained above.
Reply to Objection 3. The Philosopher speaks of the lower sensitive appetite which can be moved by the superior intellectual appetite, because it belongs to the same nature of the soul, and because the inferior appetite is a power in a corporeal organ. But this does not apply to the angels.
Source: Summa Theologica (New Advent)