Even though I've been working with IT for many years now, I'm relatively new at HTML scripting. So please bear with if this is a stupid question.

Why do I need the <html> and <body> tags when writing a html script?

I understand their uses to the extend that <body> is the "body"-part of the page, and usually comes right after <head> - and <html> is just a tag to specify which kind of language I'm using. But what happens if I leave them out? What difference do they make?

If I make a very simple index.html containing the following:

<title>Page title</title>
<h1>Headline of page</h1>
<p>Text on page</p>
...it works just fine. What difference would it do to to add <body> and <html> tags to the code?

Thanks in advance!