At least on WordPress, when the blog publishes an article it appears in your Mastodon etc timeline, and you can comment on it by replying to it directly in the timeline.
I don't know how Ghost is going to do it, but at least on WordPress the owner of the blog has a choice of ways to display the article, either full text, or an excerpt with a link, or just a link. If it's full text, Mastodon hides most of it with a "read more" button to reveal the whole thing.