This vision of the tree with a rod of iron leading to it is similar to a dream Joseph Smith, Sr. had, which his wife, Lucy Mack Smith, recorded in her history. That was one of several dreams that he had and the similarities are striking. However, they were written down long after the fact, and long after the Book of Mormon had been published. Thus, it is quite likely that they are similar because Lucy’s memory colored the similar dream her husband had with the details from the more recent and more familiar dream recorded in the Book of Mormon.
Both dreams had something to hold on to next to the path, but Joseph Smith, Sr.’s dream had a rope rather than a rod of iron. The rod of iron certainly indicates precision and permanence. Perhaps those are the images that are more important than the rigidity of the rod.
The rod of iron is next to a strait and narrow path. This language echoes Matthew 7:14: “Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.” In other locations in the dictation of the Book of Mormon, the homonym straight is interchanged with its sound-alike. The use of strait in Matthew is parallel to narrow. It sets up two images that would be well-known; a gate and a path. In both cases, they do not accommodate large numbers, and strait and narrow are used as synonyms.
Lehi’s path is accompanied by what is presumed a straight (not curved) rod of iron. The imagery of Lehi’s dream is a wider path that accommodates many who will begin. It assumes that it is possible for many to achieve the joy at the end of the path. The dream will discuss why that doesn’t happen.
Thus, we have borrowed language from the New Testament without borrowing the concepts behind the use of the phrase in the New Testament. The New Testament encouraged the relatively few believers as they worked their way to their heavenly reward.
Lehi speaks of the larger issue of those who have the opportunity for that reward, but find ways to decline it.