The following quote was taken second hand from the book The Trellis and the Vine.

[Some] have been my hearers eight or ten years, who know not whether Christ be God or man, and wonder when I tell them the history of his birth and life and death as if they have never heard it before…I have found that some ignorant persons, who have been so long unprofitable hearers, have got more knowledge and remorse in half an hour’s close discourse, than they did from ten years public preaching. I know that preaching the gospel publicly is the most excellent means, because we speak to many at once. But it is usually far more effectual to preach it privately to a particular sinner.

Let me hear your guesses in the comments section.