What meaneth the rod of iron which our father saw, that led to the tree?

father - 13 occurrences in 12 verses - 1 Nephi 15:1, 2, 7, 12, 13, 17, 18, 21, 23, 26, 27, 30

father saw - 4 occurrences in 4 verses - 1 Nephi 15:21, 23, 26, 27