Reply Obj. 2: This argument considers the adjuration which imposes an obligation.
Reply Obj. 3: To adjure is not to induce a man to swear, but to employ terms resembling an oath in order to provoke another to do a certain thing.
Moreover, we adjure God in one way and man in another; because when we adjure a man we intend to alter his will by appealing to his reverence for a holy thing: and we cannot have such an intention in respect of God Whose will is immutable. If we obtain something from God through His eternal will, it is due, not to our merits, but to His goodness. _______________________
SECOND ARTICLE [II-II, Q. 90, Art. 2]
Whether It Is Lawful to Adjure the Demons?
Objection 1: It would seem unlawful to adjure the demons. Origen says (Tract. xxxv, super Matth.): "To adjure the demons is not accordance with the power given by our Saviour: for this is a Jewish practice." Now rather than imitate the rites of the Jews, we should use the power given by Christ. Therefore it is not lawful to adjure the demons.
Obj. 2: Further, many make use of necromantic incantations when invoking the demons by something Divine: and this is an adjuration. Therefore, if it be lawful to adjure the demons, it is lawful to make use of necromantic incantations, which is evidently false. Therefore the antecedent is false also.
Obj. 3: Further, whoever adjures a person, by that very fact associates himself with him. Now it is not lawful to have fellowship with the demons, according to 1 Cor. 10:20, "I would not that you should be made partakers with devils." Therefore it is not lawful to adjure the demons.
On the contrary, It is written (Mk. 16:17): "In My name they shall cast out devils." Now to induce anyone to do a certain thing for the sake of God's name is to adjure. Therefore it is lawful to adjure the demons.
I answer that, As stated in the preceding article, there are two ways of adjuring: one by way of prayer or inducement through reverence of some holy thing: the other by way of compulsion. In the first way it is not lawful to adjure the demons because such a way seems to savor of benevolence or friendship, which it is unlawful to bear towards the demons. As to the second kind of adjuration, which is by compulsion, we may lawfully use it for some purposes, and not for others. For during the course of this life the demons are our adversaries: and their actions are not subject to our disposal but to that of God and the holy angels, because, as Augustine says (De Trin. iii, 4), "the rebel spirit is ruled by the just spirit." Accordingly we may repulse the demons, as being our enemies, by adjuring them through the power of God's name, lest they do us harm of soul or body, in accord with the Divine power given by Christ, as recorded by Luke 10:19: "Behold, I have given you power to tread upon serpents and scorpions, and upon all the power of the enemy: and nothing shall hurt you."