Textual: It is interesting that Nephi's instructions to Jacob should so clearly define the nature of the record, and perhaps in retrospect, define also Nephi's record. Jacob is given four categories of information that should be written on this set of plates. First, history - but only "lightly" (verse 2). The next three are: "preaching which was sacred, or revelation which was great, or prophesying."
Indeed, Nephi's record follows this general outline of topics, with far less history than we might want, an accounting of revelation (the tree of life dream), prophesying (parts of the Tree of Life dream as well as his prophetic extrapolation of Isaianic theme) and preaching (some record of his own less formal speeches to his brothers, and the record of Lehi's final blessings and Jacob's speech). Jacob will faithfully follow that mold, presenting again some history (so lightly as to be painful to the historian), revelations, and preachings.
It is not quite clear what Jacob means by engraving the "heads" of these things. It is tempting to suppose that the writing system had been modified in a Mesoamerican location to a Mesoamerican style which indeed had "heads" representing some syllables. While the majority of the hieroglyphic texts in Mesoamerica date from the Classic period. which postdates the Book of Mormon the antecedents of that language were developed earlier, with seminal forms being found in the same general vicinity as the proposed Nephite populations. In Mesoamerican literature, those lands were part of the Epi-Olmec area, and were known to have hieroglyphic writings of which a few precious samples have been preserved.
In spite of this intriguing possibility, the more likely meaning of "heads" in this text is that of a synopsis of the most important aspects rather than a full treatment. As we will find out, the plates have limited size, and Nephi has used most of it. It is therefore probable that Nephi was urging some restraint on the quantity while focusing on the quality of the content.
John A. Tvedtnes has suggested that the use of the word "heads" in this context might be a reflection of an underlying Hebrew structure in the Book of Mormon: "The term head seems out of place. We would expect something like most important to be used. But the expression is readily explainable in terms of Hebrew. The Hebrew word for the head of the body is sometimes used to describe things as chief (see Deuteronomy 33:15; Psalm 137:6; and Proverbs 1:21) or precious (see Amos 6:1; Song of Solomon 4:14; Ezekiel 27:22). This is probably the sense in which Jacob used the word." (Tvedtnes, John A. "The Hebrew Background of the Book of Mormon." In: Rediscovering the Book of Mormon. Ed. John L. Sorenson and Melvin J. Thorne. FARMS, 1991, p. 90).
This presents an interesting possibility, but for all of that has been written on the Hebrew language background of the Book of Mormon, the evidence is still inconclusive, having almost as much possibility of derivation from KJV language as from an original Hebrew. It is an area that will receive much more attention.
Narrative: The final phrases of this verse are crucial to understanding the verses that follow. In some ways, it was an unfortunate cutting of verses that allows such critical information to be separated from its content by the artificial conception of the verse. Jacob focuses on Nephi's instruction that the Messiah be the focus of the record. This should be done "for the sake of our people," the particular phrase that is explained in the next verse.