One of the reasons why people want to learn Latin is because of ecclesiastical reasons. The Vatican still uses Latin and has been doing so for centuries. Here are a couple of books that are specifically geared for ecclesiastical or ‘church’ Latin:
A Primer of Ecclesiastical Latin by John F. Collins is ideal for learners who like to learn Latin a little at a time because it introduces grammar concepts at a slow place, while building your vocabulary. The lessons in the book are cumulative, which means that you can’t skip chapters. This Book also provides macrons to mark long vowels. Not all books provide macrons, so this Book is actually a good resource. It also has large type with large margins, which are good for writing notes.
If you’re looking for an ecclesiastical dictionary for Latin, then you might want to take a look at the Dictionary of Ecclesiastical Latin by Leo F. Stelten. Some Latin dictionaries are solely focused on Classical Latin, so this is another good dictionary to have to supplement other dictionaries. In addition to providing the definition of ecclesiastical terms, there is good coverage of the idiomatic usages of words. The one bad disadvantage of this dictionary is that you can’t look up words in English to Latin. This is only a Latin to English dictionary.
Consecrated Phrases: A Latin Theological Dictionary : Latin Expressions Commonly Found in Theological Writings (Reference Works) by James T. Bretzke is a good book for those who want some context into some of the ecclesiastical phrases that are used in Latin. It’s a good book for those who are not Catholics and have no knowledge in canon law. All the entries are arranged alphabetically and have the literal translation into English and the theological meaning of the term as well.
Prima Latina Student Book: Introduction to Christian Latin by Leigh Lowe comes with a CD so that you can hear the actual differences in pronunciation between ecclesiastical and classical Latin. It’s a book that was originally designed for kids, but adults will appreciate the slow pace of the book as well. The Book also contains some basic chants and some prayers in Latin, so if you’re someone interested in that this Book is also suitable.