Textual: The separation into verses makes the first phrase of this verse difficult. In what is their joy? If we read verses 8 and 9 together the phrase makes a little more sense, for the joy would then be the resolution of the conflict between the need and the oath, which is the sons taking up arms. The “one thing in which we may have great joy” is that the defense of the nation was assisted without the need of violating a sacred oath.
Geographic: In Sorenson’s mapping of the Book of Mormon cities, Judea would lie upstream from Zarahemla. It creates a barrier to access to Zarahemla from the south through a pass that connects to the city of Antiparah. While not on the direct line between Zarahemla and Manti, it was clearly a city strongly enough defended that it could not be passed by. Thus these young men are being sent into the first defense behind the front lines. This is a critical area because the Lamanite incursion is coming through the valleys from the south and west and are separated from Zarahemla by the strength of Judea.