Mosiah 25:15

And it came to pass that 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.

Alma spoke to them when they gathered in large groups. He went from one group to another. He taught them to repent and have faith in the Lord.

Alma spoke to the large crowds, moving from one group to another, teaching about repentance and faith in the Lord.