Albert Barnes Commentary 1 Chronicles 12:18

"Then the Spirit came upon Amasai, who was chief of the thirty, [and he said], Thine are we, David, and on thy side, thou son of Jesse: peace, peace be unto thee, and peace be to thy helpers; for thy God helpeth thee. Then David received them, and made them captains of the band." — 1 Chronicles 12:18 (ASV)

Amasai - The marginal reference identifies him with Amasa, David’s nephew, but it seems unlikely that David would have distrusted a band led by his own nephew.

The passionate earnestness of Amasai’s speech is clearly evident in the original text and is better understood by omitting the words that some English translations add in italics for clarity. Here, as in 1 Chronicles 12:8–15, we clearly have the actual words of a very ancient record.