Every week, somebody asks for such a simple blog feature.
How do I have a single blog post always displayed, for the home page?
There are many things that Blogger has yet to provide, and this is one. A blog, by definition, contains a dynamic home page, with the most current posts displayed.
Today (sorry, too late!), if you view this blog, this post will be displayed, at the very top of the home page. Tomorrow, this post will be displayed, just not at the top of the home page. In a couple weeks, this post will not be displayed on the home page, at all. That is how blogs work. If you want to display anything else, you don't have a blog.
That's the purist position, anyway. A blog is simply a web site with the latest posts displayed on home page (the main page), and hidden older posts (the archives).