Make sure that the intro is safe for public consumption and then add a "read more" break, so that registered members can read the full article.
If a non-member clicks on the article title or the read more link, they will be redirected to the login page - this demonstrates that you can show some info without compromising the integrity of the site. I've shown an article in this way here because the main Coaching menu item is a Section Blog that will show all the articles within the Coaching Section - and half of this section is not intended for public view.