John Broadus offers this excellent advice on the reading habits of ministers (from his Lectures on the History of Preaching, 230-31).

I think that young men should be specially exhorted to read old books. If you have a friend in the ministry who is growing old, urge him to read mainly new books, that he may freshen his mind and keep in sympathy with his surroundings. “But must not young men keep abreast of the age?” Certainly, only the first thing is to get abreast of the age, and in order to this, they must go back to where the age came from, and join there the great procession of its moving thought.