When Lehi told his family of his vision, Nephi desired to see it for himself. Because of his great desire and unwavering faith, the Spirit visited him and showed him the dream. When Nephi is witnessing the vision, the thing that Lehi talked about are explained. The symbolism is made clear.
The iron rod is one of these symbols. In the vision, Nephi sees the iron rod along the straight and narrow path, extending to the tree of life. The multitudes of people in the dream are following the path to the tree by holding on to the rod of iron. Mists of darkness envelope the people. Many of them let go of the rod and become lost. But those who hold tight to the rod eventually make it to the tree of life and eat of its fruit.
Nephi understood this symbolism.
And it came to pass that I beheld that the rod of iron, which my father had seen, was the word of God, which led to the fountain of living waters, or to the tree of life; which waters are a representation of the love of God; and I also beheld that the tree of life was a representation of the love of God. (1 Nephi 11:25)
So what is the word of God? The scriptures, naturally. But what exactly are the scriptures? The Bible, the Book of Mormon, and modern-day revelation. Essentially, the words of God and Jesus Christ and the prophets.
Nephi, the same that saw his father’s vision, said,
Wherefore, I said unto you, feast upon the words of Christ; for behold, the words of Christ will tell you all things what ye should do. (2 Nephi 32:3)
The words of Christ and the words of His prophets (which are the same) will tell us all things that we should do. And if we should heed the words of the prophets now passed, then surely all the more reason to heed the words of the living prophets.
I testify that holding strongly to the word of God in His holy scriptures will keep us on the straight and narrow path to eternal life. I know that we also have living prophets today, found only in The Church of Jesus Christ of Latter-day Saints. We must listen to their counsel just as thoughtfully as we study the words of their ancient predecessors. The iron rod leading to the tree of life is indeed the word of God. It will safely guide us through.