4 Nephi 1:38

And it came to pass that they which rejected the gospel, were called Lamanites, and Lemuelites, and Ishmaelites; and they did not dwindle in unbelief, but they did wilfully rebel against the gospel of Christ; and they did teach their children that they should not believe, even as their fathers, from the beginning, did dwindle.

The people who rejected the gospel were called Lamanites, Lemuelites, and Ishmaelites. They did not slowly lose their faith. They chose to turn against Christ’s gospel on purpose. They taught their children not to believe. This was just like their fathers had slowly lost faith long ago.

Those who rejected the gospel became known as Lamanites, Lemuelites, and Ishmaelites. They didn’t gradually drift away—they deliberately rebelled against Christ’s gospel, teaching their children to reject the faith just as their ancestors had slowly lost theirs generations ago.