Helaman 3:24-26 describes how thousands of people decided to unite themselves to the church and the record even calls it tens of thousands. The church prospered exceedingly and the priests and teachers were astonished beyond measure.
Only two years later (v33), pride begins to enter the church and Mormon uses interesting language—“ not into the church of God, but into the hearts of the people who professed to belong to the church of God” (emphasis added). That indicates he is a little skeptical of the level of conversion of some of the people who joined the church in such great numbers.
In v34, we learn the proud members begin persecuting their humble brethren in the church.
By Helaman 4:1—five years after so many people joined the church—there were many dissentions in the church and a contention among the people with lots of bloodshed. So those who were not sincere in the church could not maintain the façade. Mormon does not state this, but it is easy to see that joining the church for any other reason than true conversion and commitment to Christ is not a firm foundation.
I think Mormon’s observation of the mass conversions is telling:
Thus we may see that the Lord is merciful unto all who will, in the sincerity of their hearts, call upon his holy name. (Helaman 3:27)
Sincerity is the key work there. Some among the number of converts may not have been sincere, and they would not be the ones receiving the Lord’s mercy. The Lord is not fooled by empty profession and vain posturing and parading.
For those who have to go through persecution from the proud and insincere, Mormon says,
Yea, we see that whosoever will may lay hold upon the word of God, which is quick and powerful, which shall divide asunder all the cunning and the snares and the wiles of the devil, and lead the man of Christ in a strait and narrow course across that everlasting gulf of misery which is prepared to engulf the wicked (Helaman 3:29)
For those who are sincerely converted, it is like taking a strait path through a gulf of misery to be surrounded by hypocrites in the true church and to suffer at their hands. The only way they can stay steadfast is to lay hold on the word of God and keep going.
I hope we never fall into pride and hypocrisy and persecution of our fellow members. Also, in every church ward I have been in I have been blessed to be around sincere members who are doing their best. I hope that if we ever find ourselves in a ward where members are not so sincere we can hold on our way and stay the course.