5 For though the preacher may have great ability (and this one would only find in a few), not even in this case is he released from perpetual toil. For since preaching does not come by nature, but by study, suppose a man to reach a high standard of it, this will then forsake him if he does not cultivate his power by constant application and exercise. So that there is greater labor for the wiser than for the unlearned. For there is not the same degree of loss attending negligence on the part of the one and the other, but the loss is in exact proportion to the difference between the two possessions.
For the latter no one would blame, as they furnish nothing worth regarding. But the former, unless they are constantly producing matter beyond the reputation in which all hold them, great censure attends on all hands; and besides these things, the latter would meet with considerable praise, even for small performances, while the efforts of the former, unless they be specially wonderful and startling, not only fail to win applause, but meet with many fault-finders. For the audience set themselves to be critics, not so much in judgment of what is said as of the reputation of the speaker, so that whenever any one excels all others in oratorical powers, then especially of all others does he need laborious study.
For this man is not allowed to avail himself of the usual plea which human nature urges, that one cannot succeed in everything; but if his sermons do not throughout correspond to the greatness of the expectations formed, he will go away without having gained anything but countless jeers and censures; and no one takes this into consideration about him, that dejection and pain, and anxiety, and often anger, may step in, and dim the clearness of his thoughts and prevent his productions from coming from him unalloyed, and that on the whole, being but a man, he cannot be constantly the same, nor at all times acquit himself successfully, but naturally must sometimes fall short of the mark, and appear on a lower level of ability than usual.
None of these things, as I said, are they willing to take into consideration, but charge him with faults as if they were sitting in judgment on an angel; though in other cases, too, a man is apt to overlook the good performances of his neighbor, though they be many and great, and if anywhere a defect appears, even if it be accidental, even if it only occur at long intervals, it is quickly perceived, and always remembered, and thus small and trifling matters have often lessened the glory of many and great doings.
Source: On the Priesthood (New Advent)