Mosiah 28:3

"Now they were desirous that salvation should be declared to every creature, for they could not bear that any human soul should perish; yea, even the very thoughts that any soul should endure endless torment did cause them to quake and tremble."

In chapter 27 Alma and the sons of Mosiah were visited by and angel and were brought back to the light. They were so wicked, and so unhappy in their awful state. Since they experienced such a joyful change they wanted all people to have what they had. Thus, they were desirous to preach the gospel to the Lamanites. They had so much love for all man that they wanted to share true joy with them. They were the best missionaries, because they were truly concerned for the welfare of their brothers and sisters.