Verses 6 through 9 are a summary of the sons of Mosiah traveling to the land of Nephi where the Lamanites lived. These verses reiterate the superscription and add a little more general information. To be instruments in the Lord’s hand (v. 9) is to do his work, and the sons of Mosiah had been given the priesthood authority to do that work. The Lord’s work is “to bring to pass the immortality and eternal life of man” (Moses 1:39). The bringing the Lamanites to a knowledge of the truth and overcoming their incorrect traditions was recognized by Mormon as a very difficult assignment, as shown by the phrase, “if it were possible” (Alma 17:9).
The Spirit giving them comfort (v. 10) was probably an assurance they received that they would be able to accomplish the seemingly impossible task of converting the Lamanites. That assurance came from “his Spirit (v. 10), or the Holy Ghost. Jesus identified the Comforter as “the Holy Ghost, whom the Father will send in my name, he shall teach you in all things” (John 14:26). The phrase, “the Lord said to them also” (Alma 17:11; italics added) strongly suggests that the instructions that followed were also given by the Holy Ghost.
The third requirement for being an effective missionary is found in the Lord’s admonishment to the sons of Mosiah to be good examples of him. This example was to be met by being patient in long-suffering and afflictions. A missionary must be willing to endure persecution. The Lord will thus make them instruments in his hands, and they will be his servants. The servant must be willing to “take up his cross which is to deny himself (or herself) of all ungodliness, and every worldly lust, and keep [Christ’s] commandments” (JST, Matthew 16:26) in order to bring salvation to many souls (Alma 17:11). These instructions from the Spirit to the sons of Mosiah and their companions gave them the courage to embark on their mission to the Lamanites (v. 12).
We do not know how many others were with the sons of Mosiah. There were four sons: “Ammon and Aaron, and Omner, and Himni” (Mosiah 27:34). We do know that Muloki and Ammah were with Aaron in the land of Middoni.