Bolstered by the Lord’s blessing of comfort (verse 10), the brothers begin their missionary journey. Their mission was to take the gospel to the Lamanites, and there were many of them. They split up so that they could go to different people. This was done under inspiration, and the Lord knew both the different peoples that would receive the word as well as the fact that a much smaller group of men posed much less of a threat than the entire group of armed men who had come to the Lamanite lands.
When they say that they trusted that they should meet “at the close of their harvest,” this means the end of their missionary journeys. The conversion of souls is often referred to as a harvest, and they are expecting that success, and that they will all survive to be reunited at some point when they have accomplished their mission.