Identify any possible newsworthy themes in your Christian book that might be of interest to newspapers, magazines and broadcasters. For example, if you are writing about how faith helped you through difficult times it might make a good feature article for a magazine. Topics that journalists might pick up are faith and relationships, faith and money and faith and society's problems. Write a press release, including the main news hook at the top, with contact details and use a free press release distribution service to get the message out.
Put up a simple website to market the book. You can pay someone to do this for you or use some of the free templates available on the Internet. You will need a picture of the book cover with some compelling copy about why your book adds to the Christian debate. Include details of how people can purchase the book.
Target local Christian bookstores and visit them and ask them to stock the books on a "sell or return policy," which means they return any unsold stock to you after an agreed period of time. Ask them if you can hold a book-signing event. Write to bookstores and include a copy of your press release and a cover letter. Do not confine yourself to the specialists alone though. Approach the wider, nonreligious book publishing sector too as there might be more opportunities for sales.
Tell people about your book at local churches and see if there are any opportunities to give talks and "spread the word" in your local area. Word of mouth is a sound marketing technique and has helped many books take off. Contact local schools and ask them if they would like an author's visit. This will probably not lead directly to sales, but it will help build a presence.
Find out whether there are any local Christian events or conferences where you could attend and give out some pamphlets and other information about your book. Avoid selling directly but, instead, chat to attendees and present marketing material in a subtle way.
Look into marketing via social media, such as Facebook and Twitter. You could find yourself with a large following on Twitter quickly. Make tweets regularly about your book and how it is performing. If your press release is picked up, for example, you can tweet about it.
Consider offering the book as a downloadable product from the Internet or as an audio product. This approach is still quite novel and will give your marketing an "edge." You can also offer a preview of the book or the first few chapters online to tease readers and entice them to buy the entire book.