The Golden Rule: Your feed IS ALREADY an ad
Just like an email subscription, or a direct-mail piece, your RSS feed allows your brand name, your content, your services to be delivered right into people’s “homes”- their home pages, their email box, or their RSS reader. If you are blogger, your feed is an ad for you, your thoughts & skills - if you are a bigger company - it makes sure that people see whatever it is that you are good at, on a regular basis.
Don't miss the subtle distinction. Gatz is not saying, "Your RSS feed should be an ad." He's saying it's already an ad. What's the difference? An RSS feed that's built as traditional advertising, full of marketing-speak, will not earn a customer's attention. The feed has to be full of information that's interesting to your audience first. Concentrate on the content of the feed. The advertising aspect will follow without your having to worry about it.