There were certain things Alma wanted exposed and taught and certain things he did not want made known. Alma wanted those things made known that illustrated the lesson of the ages-that whatsoever nation upholds secret combinations to get power and gain shall be destroyed in the due time of the Lord (see Ether 8:20-22).
He wanted his people to know of the secret murders, of their plunderings and other wicked dealings, in order that the Nephites might have sufficient understanding to discern and eradicate these practices when they surfaced among them. He asked specifically that Helaman retain in his possession (for safe keeping) the mechanics of the works of wickedness-the secret oaths and covenants, “their agreements in their secret abominations” (verses 27, 29)-in order that such things not get out and be propagated among the Nephites.
Although Helaman was true to his charge, secret combinations emerged among the Nephites through an independent revelation from Satan to man (see Helaman 6:25-28).