Over at Unashamed Workmen, there are a number of great quotes on the vital place of prayer in preaching. The one that really stood out was in the comments section. I think this quote expresses perfectly why we need to plead with the resurrected Jesus to pour out his Spirit on us before we dare think of preaching:

“This divine unction is the one distinguishing feature that separates true gospel preaching from all other methods of presenting truth. It backs and interpenetrates the revealed truth with all the force of God. It illumines the Word and broadens and enrichens [sic] the intellect and empowers it to grasp and apprehend the Word. It qualifies the preacher’s heart, and brings it to that condition of tenderness, of purity, of force and light that are necessary to secure the highest results. This unction gives to the preacher liberty and enlargement of thought and soul—a freedom, fullness, and directness of utterance that can be secured by no other process.”

—Power Through Prayer by E. M. Bounds