Alma 35:16

therefore, he caused that his sons should be gathered together, that he might give unto them every one his charge, separately, concerning the things pertaining unto righteousness. And we have an account of his commandments, which he gave unto them according to his own record.

So he had his sons come together. He wanted to give each one his own message about doing what is right. We have a record of what he told them.

So he called his sons together. He wanted to give each one personal counsel about living right. We have a record of what he told them—his own account of those conversations.