Declare JSTL variable an call it

I'm new in JSTL. I make a so basic program: setting variable and then use it:

<c:set var="message" value="Hello JSTL !" />
<c:out value="${message}" />
<h1>${message}</h1>

I expected that everything will work fine but I don't know why nothing displayed. Is my variable wrong declared? Or may be wrong called?