Thomas Aquinas

“ 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.
Art. 1 - Whether it is lawful to adjure the demons? Objection 1: It would seem unlawful to adjure the demons. ”

“ First, by way of appeal made to God, and this relates to those who work miracles by calling on God: secondly, by way of compulsion, which relates to the devil, who uses the irrational creature for our harm. This is the kind of adjuration used in the exorcisms of the Church, whereby the power of the demons is expelled from an irrational creature. But it is not lawful to adjure the demons by beseeching them to help us. ”

“ Accordingly when either of these orderings is confirmed by something Divine it is an adjuration. Yet there is this difference between them, that man is master of his own actions but not of those of others; wherefore he can put himself under an obligation by invoking the Divine name, whereas he cannot put others under such an obligation unless they be his subjects, whom he can compel on the strength of the oath they have taken. ”

“ I answer that, Irrational creatures are directed to their own actions by some other agent. Now the action of what is directed and moved is also the action of the director and mover: thus the movement of the arrow is an operation of the archer. ”

“ 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 Lk. ”