The Amalekite reveals the doctrinal difference between the Nephites and the Nehors, first by denying an important doctrine, then by denying that there is any evidence for it, and finally by impugning the tradition that would encourage belief in that doctrine.
By stating that these are “thy fathers and also… our fathers,” the Amalekite is not only dismissing belief in the Atoning Messiah but also in revelation (“concerning… that which is to come”).