It is a preacher’s task to make the Gospel understood by his hearers.
“So they read in the book in the law of God distinctly, and gave the sense, and caused them to understand the reading” Neh 8:8.
He must begin by making himself understood. If you cannot understand what a preacher is saying, it is usually his fault, not yours. Many people needlessly reproach themselves for not understanding the preacher – it is his task to make himself understood.
One way of checking how much attention the preacher gives to this task is to listen to his public announcements. Are they clear? Do they miss out essential details – date, time, location, etc. I heard a minister at a funeral announcing the place of the cemetery many miles away, but he didn’t mention the time of the burial. This shows carelessness to consider the message from the point of view of his audience. If preachers cannot make their public notices hearer-friendly, it is unlikely that their sermons will be meaningful to their hearers.