When we see the phrase “things to come” in the Book of Mormon, it is most often associated with the prophecies of the coming of the atoning Messiah. Thus, the question about what happens after death is not the answer to their question about the things to come, but rather the transition into the answer.
Humankind understands that we must die, and ancient peoples were much more personally acquainted with death than are modern western cultures. In modern western cultures, people die in hospitals, in clinics, in hospices. In the ancient world they died at home. In the modern world we live longer than ever before. In the ancient world, reaching the age of forty meant that one was old, and perhaps older than most. Thus, people died sooner, and closer. Questions about death readily came to mind.
Jacob cannot answer the question of how we shall see God after we are dead without explaining the mortal mission of the Messiah. Therefore, he begins that story.
Modern Christians might see this as an abrupt shift, to move the declaration of Jehovah, to a question about death, and to the answer in Jesus. For Jacob, however, there was so such shift in understanding. Note that he says: “for it behooveth the great Creator that he suffereth himself to become subject to man in the flesh, and die.” The god of the Book of Mormon is Jehovah. Jehovah is the being who left the celestial realm to become human, to become Jesus.