To perform missionary work alone is certainly not the typical pattern. The text does not give us an indication why they didn’t travel in pairs, but a couple of reasons may be that they could cover more ground and that they would be less threatening to the Lamanites if they came alone. The problem is that it would take great courage to walk into a Lamanite city with no companion, knowing that you are completely at the mercy of the people you meet.
Spencer W. Kimball
“What are we to fear when the Lord is with us? Can we not take the Lord at his word and exercise a particle of faith in him? Our assignment is affirmative…to carry the Gospel to our enemies, that they might no longer be our enemies.” (Ensign, June 1976. p. 6 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, p. 283)