Below is a quote from St. Augustine. It captures beautifully my own understanding of writing and delivering a sermon. It is from today’s Office of Readings if you want to read the whole thing.
In my search for a way to let this message reach you, so that the word already in my heart may find place also in yours, I use my voice to speak to you. The sound of my voice brings the meaning of the word to you and then passes away. The word which the sound has brought to you is now in your heart, and yet it is still also in mine.
From a Sermon by St. Augustine