If one's qualification is merely that of a librarian, one should not be a pastor nor a preacher (maybe not even a Christian).
A preacher's duty involves having read a great deal of books, but absolutely not limited to the ability to recommend books to others. In fact, it is rarely a good idea to recommend books to those who never ask for them in the first place.
Therefore, one must be articulate enough to communicate an idea, not merely giving citations.
What principle of the Bible am I applying here? Perhaps Matthew 25:14-30, the Parable of 10 talents.