When Nephi uses these words, they become testimony of his status as prophet. All God’s prophets are similarly possessed with a “sharp sword” because we can cut ourselves upon their words. We must handle words from a prophet with great care. They can damn us, or bless us, depending upon our willingness to give heed to them.
The image of being hidden in the hollow of God’s cupped hand is a powerful symbol to the sensitive mind. It suggests Temple typology, protection, and intimacy with God. To be “hid,” in particular, suggests God’s power to protect us when we rely in faith upon Him. The threats from this world are nothing if God will “hide” us from them.
A polished shaft has been fashioned, or worked upon. For God to “polish” us requires His personal attention to refining experiences in our lives. It reminds us of Nephi’s earliest words, but it also suggests there will be effort; both from God and from the individual. The result, however, will be the refinement of a human soul.