The semicolon is described here as the “most feared punctuation on earth.” Although there can be many fine points with semicolons, just this goes a very long way: A semicolon lets you join two sentences a little more closely than if there were just a period between them. It is a nice little tool for just that, and it helps improve writing variety.  The referenced link points to a good, compact resource; here’s another – hey, how about that, a semicolon! We give these links to the kids.