One hit wonders

A while ago now somebody asked me what was my one sermon? I can’t remember where he got the quote from but he was saying that somebody had once said most preachers have one main sermon, not that they always preach the same or the same type of thing but if you look at their preaching there is often a common theme that can be spotted. This got me thinking is this true and if so what is my common theme? I came to the conclusion that for me I probably speak more often about the fact that as Christians if we are following God and the calling he has placed on our lives, He can use us to make a significant difference in this world, we might not be Billy Graham, or Mother Teresa but that doesn’t mean that our impact is not great or not as important , we can all make a difference. What's your one sermon?