How can I display the contents of the blog page text for the first page only?

Looking at the pagination buttons at the bottom of a blog, it is clear that the pagination plugin knows if it is at the beginning, or end, of the collection of blog pages.

When digging into the plugin's template '/templates/pagination.html.twig', we can see the plugin uses the following to determine if it is NOT at the beginning of the collection:

{% if pagination.hasPrev %}

where 'pagination' is defined at the top as:

{% set pagination = pagination|default(page.collection.params.pagination) %}

Looking at the code of the plugin, it seems to extend the 'params' property of a collection. It adds a 'pagination' property, which provides methods like 'hasPrev()' and 'hasNext()'.

Solution:
You could try if the following works for you. Add these lines to template 'blog.html.twig':

{% if not page.collection.params.pagination.hasPrev %}
    <h1>The text I only want to show on page 1</h1>
{% endif %}

I don't know for Helium/Gantry, but is does work for Quark.... ;-)