The Philosophy of Natural Magic, by Henry Cornelius Agrippa, L. W. de Laurence ed. , at sacred-texts.com
The passions of the mind are much helped, and are helpful, and become most powerful by virtue of the Heavens, as they agree with the Heaven, either by any natural agreement or by voluntary election. For, as saith Ptolemy, he which chooseth that which is the better seems to differ nothing from him who hath this by nature. It conduceth, therefore, very much for the receiving of the benefit of the Heavens, in any work, if we shall, by the Heaven, make ourselves suitable to it in our thoughts, affections, imaginations, deliberations, elections, contemplations, and the like. For such like passions do vehemently stir up our spirit to the likeness of the Heavens and expose us and ours straightway to the Superior Significators of such like passions; and, also, by reason of their dignity and nearness to the Superiors do much more partake of the Celestials than any other material things. For our mind can, through imagination or by reason of a kind of imitation, be so conformed
to any Star as suddenly to be filled with the virtues of that Star, as if it were a proper receptacle of the influence thereof. Now, the contemplating mind, as it withdraws itself from all sense, imagination, nature, and deliberation, and calls itself back to things separated, unless it exposeth itself to Saturn, is not of present consideration or enquiry. For our mind Both effect divers things by faith (which is a firm adhesion, a fixed intention, and a vehement application of the worker, or receiver) to him that cooperates in any thing, and gives power to the work which we intend to do. So that there is made, as it were, in us, the image of the virtue to be received, and the thing to be done in us, or by us. We must, therefore, in every work and application of things, affect vehemently, imagine, hope, and believe strongly, for that will be a great help. And it is verified amongst physicians, that a strong belief, and an undoubted hope and love towards the physician and medicine, conduce much to health; yea, more, sometimes, than the medicine itself. For the same that the efficacy and virtue of the medicine works, the same doth the strong imagination of the physician work, being able to change the qualities in the body of the sick, especially when the patient placeth much confidence in the physician, by that means disposing himself for the receiving of the virtue of the physician and physic. Therefore, he that works in Magic must be of a constant belief, be credulous, and not at all doubtful of obtaining the effect. For, as a firm and strong belief doth work wonderful things, although it be in false works, so distrust and doubting doth dissipate and break the virtue of the mind of the worker, which is the medium between both extremes; whence it happens that he is frustrated of the desired influence of the superiors, which could not be joined and united to our labors without a firm and solid virtue of our mind.