That is, to get to stand and preach Christ each week is a privilege beyond description, but I often feel terribly inadequate for the task. This makes me deeply appreciative for your prayers for me as I stand each week to preach. I couldn’t have expressed this struggle any better:
It is a long time since I preached a sermon that I was satisfied with. I scarcely remember ever having done so. You do not know, for you cannot hear my groans when I go home, Sunday after Sunday, and wish that I could learn to preach somehow or other—wish that I could discover the way to touch your hearts and your consciences, for I seem to myself to be just like the fire when it needs stirring—the coals have got black when I want them to flame forth!
If I could but say in the pulpit what I feel in my study, or if I could but get out of my mouth what I have tried to get into my own soul, then I think I should preach, indeed, and move your souls! Yet perhaps God will use our weakness, and we may use it with ourselves, to stir us up to greater strength.
(Good Earnests of Great Success, Metropolitan Tabernacle Pulpit, Vol. 14, Sermon #802, p. 176)
Thanks to my good friend Rob Murphey for pointing me to this.
Scott W. Kay 
On a similar note, I came across this quotation by Augustine:
“My preaching almost always displeases me. For I am eager after something better, of which I often have an inward enjoyment before I set about expressing my thoughts in audible words. Then, when I have failed to utter my meaning as clearly as I conceived it, I am disappointed that my tongue is incapable of doing justice to that which is in my heart. What I myself understand I wish my hearers to understand as fully; and feel that I am not so speaking as to effect this purpose. The chief reason is that the conception lights up the mind in a kind of rapid flash; whereas the utterance is slow, lagging, and far unlike what it would convey.” (De Catech. Rudibus, ch. II. 3).
My sentiments also.
That’s a very helpful quote from Augustine – especially when you consider that he was highly trained in rhetoric!