More power does not always mean more power. Sometimes for emphasis we need to do the opposite of the obvious:
When less is more in delivery – When we are convinced or excited, our volume tends to rise. But it can be dynamic and powerful to drop to a whisper at the point of emphasis. When worked up we easily rise in pitch, delivering our most significant material in the annoying shrill of an over-enthusiastic choirboy (but dropping the pitch to a lower tone will add emphasis without the discomfort for listening ears). And of course, when we get worked up we easily drop our foot to the floor and speed through key material. In the cold light of midweek it is easy to spot the weakness in that approach!
Variation is critical in content and delivery. One way to add variety is to be sure to look for opportunities to apply the old principle that works so well in preaching – sometimes less is more!