Custom theme: How to call archive-post.php for viewing blog posts

You don’t need to rename the archive.php as archive-post.php. Cause it is default to post for archive.php. If you have any other post type then use archive-{post_type}.php for pointing this template to this post type.

Now come to get_template_part(). It is used for breaking the large code base of the template to single part so it can be managed easily as well as be reused. So it’s better to use it. Cause it makes development and code maintain easy.

Hope that helps.