Helaman 16:5

telling them of things which must shortly come, that they might know and remember at the time of their coming, that they had been made known unto them beforehand, to the intent that they might believe; therefore as many as believed on the words of Samuel, went forth unto him to be baptized, for they came repenting and confessing their sins.

He told them about things that would happen soon. This way they could know and remember. When these things happened, they would remember they were told ahead of time. Then they would believe. So those who believed Samuel’s words went to Nephi to be baptized. They came to change and tell about their sins.

He told them about things that would happen soon, so that when these things came true, they would remember they’d been warned ahead of time and would believe. Everyone who trusted Samuel’s words came to Nephi to be baptized, confessing their sins and turning away from their old lives.