Purchase a copy of the "Songwriter's Market." This book is a valuable resource for all songwriters. It includes an extensive section for Christian music publishers with guidelines about the type of Christian songs each market publishes, where to send your submissions, how to format your submissions and what you will be paid if your songs are accepted. The market guide is updated each year, so be sure to get a current copy.
Contact Word Publishing or EMI Christian Music Group (see Resources). These are two of the biggest publishers of Christian music. Some of the artists represented by these two companies includes Steven Curtis Chapman, Amy Grant, and Michael W. Smith. You can contact either of these companies through their official Web sites. Write a query letter before you submit anything. In the letter introduce yourself, state your purpose for writing and thank the the publisher for considering your work.
Consider joining the Gospel Music Association. In addition to offering its members access to a comprehensive Christian music database that includes contact information for Christian music publishers, the Gospel Music Association offers articles about the industry and sponsors events to give Christian and gospel music writers a chance to build contacts.