Some people naively think there is no difference between written and oral communication. Many of us would agree that there is a significant difference. Yesterday I was interacting with someone who believes these two forms of communication are polar opposites. Written communication is linear, it is single channel, it is the way to go when the goal is to inform. Spoken communication is complex, it involves dozens of channels and it is the way to go when the goal is to motivate, to influence, to persuade.
With all the added channels of communication such as energy, eye contact, posture, body language, intonation, etc., preaching is an ideal opportunity to do what preaching is supposed to do. Go beyond informing listeners to influencing and motivating response to the Word of God. Preaching involves explanation of the text, but it is to be applicational explanation. If all you plan to do in your next sermon is inform, then perhaps it would be better use of your time and theirs to just write them a letter instead?