HKB
"the most excellent manner of prophecy is when a man prophesies by the mere inspiration of the Holy Ghost, apart from any outward assistance of deed, word, vision, or dream."
I answer that, The excellence of the means is measured chiefly by the end. Now the end of prophecy is the manifestation of a truth that surpasses the faculty of man. Wherefore the more effective this manifestation is, the more excellent the prophecy. But it is evident that the manifestation of divine truth by means of the bare contemplation of the truth itself, is more effective than that which is conveyed under the similitude of corporeal things, for it approaches nearer to the heavenly vision whereby the truth is seen in God's essence. Hence it follows that the prophecy whereby a supernatural truth is seen by intellectual vision, is more excellent than that in which a supernatural truth is manifested by means of the similitudes of corporeal things in the vision of the imagination.
Moreover the prophet's mind is shown thereby to be more lofty: even as in human teaching the hearer, who is able to grasp the bare intelligible truth the master propounds, is shown to have a better understanding than one who needs to be taken by the hand and helped by means of examples taken from objects of sense. Hence it is said in commendation of David's prophecy (2 Kings 23:3): "The strong one of Israel spoke to me," and further on (2 Kings 23:4): "As the light of the morning, when the sun riseth, shineth in the morning without clouds."
Reply Obj. 1: When a particular supernatural truth has to be revealed by means of corporeal images, he that has both, namely the intellectual light and the imaginary vision, is more a prophet than he that has only one, because his prophecy is more perfect; and it is in this sense that Augustine speaks as quoted above. Nevertheless the prophecy in which the bare intelligible truth is revealed is greater than all.
Reply Obj. 2: The same judgment does not apply to things that are sought for their own sake, as to things sought for the sake of something else. For in things sought for their own sake, the agent's power is the more effective according as it extends to more numerous and more remote objects; even so a physician is thought more of, if he is able to heal more people, and those who are further removed from health. On the other hand, in things sought only for the sake of something else, that agent would seem to have greater power, who is able to achieve his purpose with fewer means and those nearest to hand: thus more praise is awarded the physician who is able to heal a sick person by means of fewer and more gentle remedies. Now, in the prophetic knowledge, imaginary vision is required, not for its own sake, but on account of the manifestation of the intelligible truth. Wherefore prophecy is all the more excellent according as it needs it less.