What is the meaning of the word "heads" mentioned in Jacob 1:4? According to Mary Treat, the authors of the Theological Wordbook give this explanation for the root from which "heads" is derived:
"The root is widely used in the Old Testament with other terms in the sense of the superlative, since Hebrew does not have any simple form to express the third degree. There are many examples of this usage (Exodus 30:23) where the meaning is 'best,' 'foremost,' 'the uniquely finest,' which alone was fit for the service of God."
Understanding this Hebraism helps clarify Jacob's words. Jacob was reiterating the commandment given to Nephi about the contents of the small plates, i.e., that he should only engrave on them "the very best," or "foremost" or "the uniquely finest" of the preaching, revelation or prophecies during his lifetime. Nephi's own account of receiving this commandment is found in 1 Nephi 19:3 and confirms the meaning of the Hebraism "heads":
"And after that I made these [small] plates by way of commandment,
I, Nephi, received a commandment that the ministry and the prophecies,
The more plain and precious parts of them,
Should be written upon these plates." (Jacob 1:4)
Nephi's words, "the more plain and precious parts," equates to Jacob's use of "heads," i.e., the best, foremost, uniquely finest. [Mary Lee Treat, "The Purpose Principle in Action: "Why Heads?," in Recent Book of Mormon Developments, Vol. 2, p. 42]