In verse 10 Jacob says that there is an awful monster, which he defines as death and hell. He has quoted Isaiah as saying of Jehovah: “Art thou not he that hath cut Rahab, and wounded the dragon?” (2 Nephi 8:9). Jacob’s use of the monster in this verse is intended to invoke this verse from Isaiah. It is made even more plausible that the fact that while Jacob only mentions one monster, Isaiah has both Rahab—also known as Leviathan, or a primordial ocean monster—and a dragon—presumably an earthbound monster.
When Jacob mentions death and hell, he equates them with mortal death and the death of the spirit. In verse 12 he confirms that his definition of hell is this death of the Spirit. In Isaiah, Jehovah defeats the two monsters, and that becomes the scriptural basis for Jacob’s teaching that Jehovah will defeat death and hell.
Death has claim on the body, and hell on the spirit. Through resurrection, both death and hell must release their separate captives, which are restored to one being through the power of the resurrection.