Don’t Flatten the Gospels
Matt’s point about Gospel Harmonies also applies to epistle parallels.
If you’re preaching a passage from one of the Gospels and you blend into your sermon all the information found in the parallel passages, oftentimes the end result is a flattening out of all the Gospel accounts so that each of them is made to say exactly the same thing as all the others. In doing so, I fear that you miss out on the distinct contribution that each Gospel writer is trying to make in the context of his own Gospel.
And from the comments, Paul summarizes the point.
Preach the text not the event.