Just a note about Alma in the Book of Mormon, not of particular moment.
If one reads the Book of Mormon text of Mosiah 25 without thinking about it one may conclude that there was not a true church in existence before Alma was allowed to "establish churches throughout all the land" and given power to "ordain priests and teachers over every church". One might also think the text means that there was not baptism being practiced among the Nephites at that time.
Mosiah 25:17 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.
18 Therefore, Alma did go forth into the water and did baptize them; yea, he did baptize them after the manner he did his brethren in the waters of Mormon; yea, and as many as he did baptize did belong to the church of God; and this because of their belief on the words of Alma.
19 And it came to pass that king Mosiah granted unto Alma that he might establish churches throughout all the land of Zarahemla; and gave him power to ordain priests and teachers over every church.
20 Now this was done because there were so many people that they could not all be governed by one teacher; neither could they all hear the word of God in one assembly;
21 Therefore they did assemble themselves together in different bodies, being called churches; every church having their priests and their teachers, and every priest preaching the word according as it was delivered to him by the mouth of Alma.
22 And thus, notwithstanding there being many churches they were all one church, yea, even the church of God; for there was nothing preached in all the churches except it were repentance and faith in God.
23 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;
24 And they were called the people of God. And the Lord did pour out his Spirit upon them, and they were blessed, and prospered in the land.
But stepping back to compare to the scriptural context changes one's impressions. First off, baptism was not new among them. Nephi spoke of the essential nature of baptism back in 2 Nephi 31. And Nephi already learned that there are save two churches only, one being the church of the lamb of God, and the other being the church of the devil. The church of the lamb of God IS the church of Jesus Christ.
What Alma is doing here is administrative, not the formation of the gospel. It is a way to increase the amount of scriptural preaching that the people enjoy. Under the law of Moses there are priests that make sacrifices, and there are judges, but there is no mention in what we have that I know of about local congregations with local, frequent gospel instruction. There was the temple, and there were places the Lord set aside for making sacrifices, but in the law of Moses, teaching is presented as a family matter, where each family is to study the scriptures themselves and keep them in front of them and in their conversation throughout their day. It seems likely that some form of frequent gospel congregation meeting was still done in some form, but that it was done under primarily under the hand of the prophet before Alma, as the issue of needing more than one teacher is made clear in verse 20 "Now this was done because there were so many people that they could not all be governed by one teacher".