John of the Cross (1542-1591) was a Catholic theologian who wrote about the problem of intrusive sexual thoughts during prayer. He believed there were three possible causes for such thoughts, and one of them was simply fear of having such thoughts.
For it often comes to pass that, in their very spiritual exercises, when they are powerless to prevent it, there arise and assert themselves in the sensual part of the soul unclean motions.... These things are not, as I say, in their power; they proceed from one of three causes.
The first cause from which they often proceed is the pleasure which human nature takes in spiritual things. For when the spirit and the sense are pleased, every part of a man is moved by that pleasure.... For then the spirit, which is the higher part, is moved to pleasure and delight in God; and the sensual nature, which is the lower part, is moved to pleasure and delight of the senses....
The second cause whence these rebellions sometimes proceed is the devil, who, in order to disquiet and disturb the soul, at times when it is at prayer or is striving to pray, contrives to stir up these motions of impurity in its nature....
The third source whence these impure motions are apt to proceed in order to make war upon the soul is often the fear which such persons have conceived for these impure representations and motions. Something that they see or say or think brings them to their mind, and this makes them afraid, so that they suffer from them through no fault of their own. (Book I, Chap. IV)
[From St. John of the Cross, Dark Night of the Soul, in E. Allison Peers, ed., The Complete Works of Saint John of the Cross (London: Burns Oates & Washbourne Ltd., 1953), 338-40.]
John Sharp (1645-1714), Archbishop of York, preached a sermon before the King and Queen during Lent in 1694. The sermon was later published as a short book called The Government of the Thoughts. A portion of the sermon addressed obsessive thoughts.
[D]eeply hypocondriac [which had a broader meaning in Sharp's time] persons will be haunted with a set of thoughts and fancies, that they can by no means get rid of, tho' they desire it never so earnestly....
Sometimes they are tormented with blasphemous thoughts, and they cannot set themselves to the performance of any office of devotion, but a thousand impious fancies will come in and spoil all.
Sometimes they fancy they are guilty of several grievous crimes, which it is to be hoped, it was hardly possible they should be guilty of, nay, you cannot convince them but that they do every day commit some of these crimes [i.e. bad thoughts], because they imagine they give consent to them.
And whilst these sorts of thoughts fill their imaginations, there is not a passage in the bible that they read, nor a sermon that they hear, but they find something in it, which they do so perversely apply to their own case, as thereby to increase their trouble, but not to get any relief.
I have known several well-disposed persons, and some of them sincerely pious that have been in this condition.
What now is to be said to this? Why, it is very certain that all these thoughts and fancies are thrust upon them, and are not the free natural voluntary operations of their own minds; but the effects of vapours or hypocondriac melancholy. Nor can the persons themselves any more help their thus thinking, or fancying, than they can help the disturbances of their dreams when they have a mind to sleep quietly. Indeed we may properly enough call these fancies of theirs, their waking-dreams; as their dreams are their sleeping fancies.
Well, but now of all persons whatsoever, these people are most desirous to have rules given them for the government [i.e., controlling] of the thoughts. And I cannot blame them because their thoughts are certainly very troublesome. But truly if we would speak pertinently to their case; instead of giving them advice for the regulating their thoughts, they should rather be advised to look after their bodies, and by the help of good prescriptions to get rid of those fumes and vapours which occasion these fancies. When the cause is removed, the effect will soon cease. I do not in the least doubt, whatever these people may think of their own case, but that this is as properly a bodily disease, as a fever or fits of the falling sickness.
[From John Sharp, The Government of the Thoughts: A sermon preach'd before the King and Queen... (London : printed and sold by H. Hills, in Black-fryars, possibly 1705), 7-8 (first published in 1694).]
George Tullie, an Anglican clergyman, published a book called A Discourse of the Government of the Thoughts (London: printed for Ric. Chiswell at the Rose and Crown, 1694) in which he addressed the subject of obsessive "bad" thoughts. Tullie's ideas were similar to (and probably influenced by) John Moore.