A couple of quotes I found today on the necessity of the Spirit in preaching ministry.
All the hope of our ministry lies in the Spirit of God operating on the spirits of men - Spurgeon
How utterly dependent we are on the Holy Spirit in the work of preaching. All genuine preaching is rooted in a feeling of desperation. You go to your study. You look down at your pitiful manuscript and you kneel down and you cry, "God, this is so weak. Who do I think I am? What audacity to think that in three hours my words will be the odor of death to death and the fragrance of life to life. My God, who is sufficient for these things?" - John Piper