“Publish. Gain internal credibility by first getting external imprimatur. Professionals will believe you’re important if someone else thinks you are.”
Let’s take a look at this for a second. I can’t resist, of course.
What this pithy observation is saying is that by publishing in the “right” places, e.g., the ones that your target clients read, you will gain credibility with the publication’s readers. The fact that the magazine or journal (print or online) allows you to address their subscribers, gives you credibility with that audience, and others that hear about it or see it.
The same applies to public speaking. By picking an organization that has the audience that you desire to represent, the organization’s credibility among its members will be transferred to you by the fact that you have been allowed to address them.
That is why speaking and writing are still excellent business development tools. Of course, you could lose that "free" gift by delivering a boring speech – both content-wise or with a poor delivery – or a poorly written article.
Basically, you’ve been given a free lunch, that you best be grateful for by doing an excellent job in delivering meaningful content.