You may have a list of people who have opted in to receive more information on your topic, but have not purchased your eBook or other product. I have found that the best way to connect with them is to remind them of what your product or servive has to offer.
For example, tell them about one of your chapters and what information is included there. You will be sharing a few of the benefits with them, and if they are still interested in your topic thay may be more likely to purchase it at this time. By sharing more details of what you know and will be teaching them, it brings your list even closer to the idea of buying your information and solving their problem.