Behold, O Lord, their souls are precious, and many of them are our brethren; therefore, give unto us, O Lord, power and wisdom that we may bring these, our brethren, again unto thee.
I read this last night and thought it is the perfect missionary scripture. Now, there are a lot of missionary scriptures, but I like how this expresses the reason (their souls are precious) and the goal (that we may bring these unto thee) along with the request (power and wisdom), which shows an acceptance of the responsibility and a true desire to fulfill the call. I feel that it expresses a real understanding of the importance of the gospel and of missionary work that I could probably do to have more of.
Plus, I always appreciate a prayer for wisdom.