Other Alternatives for Promoting Your Spiritual Book
Since a spiritual book is often difficult to define for people who are not familiar with the genre, it makes sense to employ alternative techniques as well. This doesn't mean that you shouldn't send summaries of your work to the official publishing channels though. If you want to get ahead of the competition, however, you will need be a bit more aggressive.
Starting a blog on your book would be a good start. This does not guarantee that you will get visitors, but if someone is interested in your book and looks it up on a search engine, your blog might pay off. It is important that you get people to interact with your posts there though, otherwise it is no different to a normal information-oriented website.
Nowadays the vast majority of people have something to gain from a spiritual book, particularly a practical one. If you keep that in mind while promoting your work, you might be able to reach a wider audience. Sometimes people you wouldn't expect to be your readers may take interest in your work because they will seek answers to their more generic questions about life there. These are things that you can cover in an article where you talk about the main ideas of your book, to get people interested and keen on looking into it further. This is not exactly advertizing, since you don't tell them to buy your book, but it can be as effective.
Finally, it doesn't hurt to have a few copies of your book available for free (publishers tend to give the author a few copies for that purpose). These copies can be distributed to friends, prize winners, and of course reviewers. You won't make any money from that, but this strategy may help get the word out. If your book has what it takes, it may prove vital for its sales success.