Alma 46:15

and those who did belong to the church, were faithful; yea, all those who were true believers in Christ, took upon them, gladly, the name of Christ, or Christians, as they were called, because of their belief in Christ, which should come;

Those who belonged to the church were faithful. All the true believers in Christ happily took the name of Christ, or Christians. They were called this because they believed in Christ who would come.

And church members were faithful. All the true believers in Christ gladly took on the name of Christians because of their faith in the Christ who was coming.