The preacher preached his sermon, but the sermon he preached was not the only sermon that day. For everyone who attended heard it differently, and took away from the service a different sermon. Some no doubt misheard the sermon, with the result that they thought the preacher preached very badly. And some misheard the sermon to different effect, hearing profound things the preacher never said.
As Thomas Aquinas said, That which is received is received according to the capacity of the recipient.
But that's not all there is to be said on this. We mustn't forget that it is the work of the Holy Spirit not only to inspire the preacher, but to give his words effect in the hearts of the hearers, and without his ministry, all our sermons are just words.