4. Helps us clarify our own beliefs: As we study other faiths we inevitably compare our beliefs with those of others, forcing us to think through theological issues we might not have otherwise.  For example, by studying the Hindu understanding of avatars (physical manifestations of deities), I have to think through in a more detailed fashion the implications of the Christian doctrine of the Incarnation.  Essentially, by studying other faiths you are able to better appreciate the subtleties and beauty of biblical teaching. 
 
5. Helps us communicate the gospel: Every time we tell someone about the gospel of Jesus Christ we have to contextualize the gospel.  That is, we need to present the gospel in a way in which the hearer can accurately understand the message we are trying to communicate.  The gospel message does not change, but the way in which we present it does change depending on the culture and religious views of the person we are talking to.  Clearly, you will present the gospel differently to an atheist as opposed to a Mormon.  By understanding the faith of other people you will be better equipped to engage in spiritual conversations with them.
 
6. Helps missionaries develop strategies for reaching different people groups: As missionaries attempt to engage unreached people groups they must take into account the religious beliefs of that particular group.  If missionaries do not understand the beliefs of those they are trying to reach they cannot contextualize the gospel or their methods.  Moreover, by understanding the religious beliefs of their people group missionaries are better able to identify theological “bridges” or points of contact between the gospel and the group’s beliefs.  These “bridges” will in turn facilitate communication of the gospel.