Mosiah 26:6 - 26:10

Mosiah 26:6 For it came to pass that they did deceive many with their flattering words, who were in the church, and did cause them to commit many sins; therefore it became expedient that those who committed sin, that were in the church, should be admonished by the church.

In order to feel better about their decision to not follow the doctrines of the gospel, they wanted to get as many people in their camp as they could. It was those who were committing sins of all kinds that were looking for others to join with them in their sinful state. It was now time for the Church to do something about this situation of so many sinners in their ranks.
[I guess this was never a problem in the past. You were living the principles of the gospel or you were not and not a member of the Church. But now the Church is under direct attack and it must remove the evil influences of the sinful members or fall.]

Mosiah 26:7 And it came to pass that they were brought before the priests, and delivered up unto the priests by the teachers; and the priests brought them before Alma, who was the high priest.

They were taken to the local heads of the congregations, then eventually to Alma.

Mosiah 26:8 Now king Mosiah had given Alma the authority over the church.

King Mosiah had given Alma control of the Church.
[The Church never operates in a country without official permission of the government. We do not do it in secret but openly. If we cannot come in the front door, we do not come in at all until we can.]

Mosiah 26:9 And it came to pass that Alma did not know concerning them; but there were many witnesses against them; yea, the people stood and testified of their iniquity in abundance.

However, Alma did know what to do with these apostates. There were so many people complaining about their actions that Alma could not just let it go uncorrected.

Mosiah 26:10 Now there had not any such thing happened before in the church; therefore Alma was troubled in his spirit, and he caused that they should be brought before the king.

No such situation had ever happened in the Church before and Alma was not sure what to do with them. Alma sent them to king Mosiah.