All things bear record · Mosiah
2 witnesses of Christ here, and 2 further echoes from the reading.
And Alma did speak unto them, when they were assembled together in large bodies, and he went from one body to another, preaching unto the people repentance and faith on the Lord. Mosiah 25:15
Alma preaches the first principles of the gospel: faith in the Lord Jesus Christ and repentance. Verse 23 shows this faith led people to take His name.
And he did exhort the people of Limhi and his brethren, all those that had been delivered out of bondage, that they should remember that it was the Lord that did deliver them. Mosiah 25:16
Alma reminds the freed people that the Lord, Jehovah, the premortal Christ, is the One who delivered them.
How we know: Jehovah is the premortal Christ (Abraham 1:16; D&C 110:3–4)
And it came to pass that after Alma had taught the people many things, and had made an end of speaking to them, that king Limhi was desirous that he might be baptized; and all his people were desirous that they might be baptized also. Mosiah 25:17–18
Baptism is the covenant by which people come unto Christ and witness they will take His name and serve Him, as taught at the waters of Mormon.
Christ — the Anointed One
And now there were seven churches in the land of Zarahemla. And it came to pass that whosoever were desirous to take upon them the name of Christ, or of God, they did join the churches of God; Mosiah 25:23
Joining the church meant taking upon oneself the name of Christ by covenant. This echoes King Benjamin's covenant people and the sacrament prayer today.
How we know: the verse itself names Him · a footnote points to Him · a Church study aid lists it