Objection 1. It would seem that by the Divine revelation a prophet knows all that can be known prophetically. For it is written (Amos 3:7): "The Lord God doth nothing without revealing His secret to His servants the prophets." Now whatever is revealed prophetically is something done by God. Therefore there is not one of them but what is revealed to the prophet.
Objection 2. Further, "God's works are perfect" (Deuteronomy 32:4). Now prophecy is a "Divine revelation," as stated above (Article 3). Therefore it is perfect; and this would not be so unless all possible matters of prophecy were revealed prophetically, since "the perfect is that which lacks nothing" (Phys. iii, 6). Therefore all possible matters of prophecy are revealed to the prophet.
Objection 3. Further, the Divine light which causes prophecy is more powerful than the right of natural reason which is the cause of human science. Now a man who has acquired a science knows whatever pertains to that science; thus a grammarian knows all matters of grammar. Therefore it would seem that a prophet knows all matters of prophecy.
On the contrary, Gregory says (Hom. i super Ezech.) that "sometimes the spirit of prophecy indicates the present to the prophet's mind and nowise the future; and sometimes it points not to the present but to the future." Therefore the prophet does not know all matters of prophecy.
I answer that, Things which differ from one another need not exist simultaneously, save by reason of some one thing in which they are connected and on which they depend: thus it has been stated above (I-II, 65, 1 and 2) that all the virtues must needs exist simultaneously on account of prudence and charity. Now all the things that are known through some principle are connected in that principle and depend thereon. Hence he who knows a principle perfectly, as regards all to which its virtue extends, knows at the same time all that can be known through that principle; whereas if the common principle is unknown, or known only in a general way, it does not follow that one knows all those things at the same time, but each of them has to be manifested by itself, so that consequently some of them may be known, and some not.
Now the principle of those things that are prophetically manifested by the Divine light is the first truth, which the prophets do not see in itself. Wherefore there is no need for their knowing all possible matters of prophecy; but each one knows some of them according to the special revelation of this or that matter.
Reply to Objection 1. The Lord reveals to the prophets all things that are necessary for the instruction of the faithful; yet not all to every one, but some to one, and some to another.
Reply to Objection 2. Prophecy is by way of being something imperfect in the genus of Divine revelation: hence it is written (1 Corinthians 13:8) that "prophecies shall be made void," and that "we prophesy in part," i.e. imperfectly. The Divine revelation will be brought to its perfection in heaven; wherefore the same text continues (1 Corinthians 13:10): "When that which is perfect is come, that which is in part shall be done away." Consequently it does not follow that nothing is lacking to prophetic revelation, but that it lacks none of those things to which prophecy is directed.
Reply to Objection 3. He who has a science knows the principles of that science, whence whatever is pertinent to that science depends; wherefore to have the habit of a science perfectly, is to know whatever is pertinent to that science. But God Who is the principle of prophetic knowledge is not known in Himself through prophecy; wherefore the comparison fails.
Source: Summa Theologica (New Advent)