This comment sparks Jacob's discussion of the resurrection. He knows that there is something after heaven and hell. He understands that heaven and hell end in the resurrection to be replaced by kingdoms of different glories. Since the Bible speaks mostly of heaven and hell, and rarely speaks of events thereafter, this concept is important. It was taught by Job who said, And though after my skin worms destroy this body, yet in my flesh shall I see God (Job 19:26).
The context is clearly talking about seeing God after one is resurrected, but Nephi and Jacob have both learned by personal experience that one who exhibits enough faith and purity of heart can see God while in the flesh. This can only occur when the mortal body undergoes a transfiguration so that it can withstand the presence of God. As Moses explained, But now mine own eyes have beheld God; but not my natural, but my spiritual eyes, for my natural eyes could not have beheld; for I should have withered and died in his presence; but his glory was upon me; and I beheld his face, for I was transfigured before him (Moses 1:11).