I found this quote by Augustine (De consecratione, dist. 2, ch. Utrum) as I was reading the Examination by Martin Chemnitz today (vol. 2, p. 82). It is both convicting and comforting at the same time.
“Nothing more is effected by a good priest, nothing less by a bad one, because it is effected not through the merit of the one who consecrates, but through the word of its Creator and by the power of the Holy Spirit.”
I realize that Augustine is speaking about the validity or efficacy of the Eucharistic consecration, but I think that his words apply to all aspects of the Ministry of the Word. His words convict me for all the times that I believed that my skill, personality, or winsomeness added anything to the Ministry of the Word. But they also comfort me for they remind me that the efficacy of the Word is not diminished by my shortcomings (unless, of course, I was proclaiming and teaching falsely–then the efficacy of the Word would be diminished because it was not being truthfully proclaimed).