Verses 19 and 20 show two phases in the reaction of the sinful to the message of righteousness. The first is to mock, and the second is to attack. The Book of Mormon is quite instructive on the way in which the gospel can effect the unrighteous. For instance Lehi describes the impact of the words of truth:
40 O, my beloved brethren, give ear to my words. Remember the greatness of the Holy One of Israel. Do not say that I have spoken hard things against you; for if ye do, ye will revile against the truth; for I have spoken the words of your Maker. I know that the words of truth are hard against all uncleanness; but the righteous fear them not, for they love the truth and are not shaken.
The light of Christ is given to all men, and is the ultimate measure for truth. When the truth of what we hear reveals to us our separation from God, or our sinful state, the light of Christ witnesses to the correctness of the preaching. In those who are able to listen to the message of that spirit, this process can lead to repentance. The process of repentance always involves some form of moral or emotional pain (leading up to Godly sorrow). Our natural tendency is to find a way to remove the pain. For some repentance is the ultimate cleanser. For others, however, that pain of recognition that we are contrary to the will of God causes us to find ways to ignore the pain, or build up defenses against it.
The ultimate defense against the pain caused by hearing the word of God is to deny and reject the word. By denying the validity of the message, we can cover the pain we feel when we hear it. This is the process of hardening the heart. We continually build defenses against feeling the pricks of the spirit. In the first instance the people of Jerusalem mocked Lehi. In this stage they exemplify the most normal stage of hardening of the heart. It is that phase where they deny the word that they hear.
The process of hardening the heart can continue, however, and increase in the type of defense mechanism which is used. The ultimate is that the denial of the spirit is so great as to completely turn against it, and seek the life of the messenger. While taking a life is the ultimate denial, close to it are the very related tendencies to fight against the truth. Thus disaffected saints are often the most vocal in attacking the church to which they once belonged. This comes from a personal necessity to self-justify their action and to reinforce the wall built around the promptings of the spirit.
Literary analysis: Already to this point at the end of the first chapter of Nephi the phrase "and it came to pass" has occurred six times. In the Book of Mormon it will occur a total of 999 times. It occurs in the Book of Mormon with a much greater frequency that in any other body of Christian scripture, although it is found in each. In the scriptural texts, the next highest number of occurrences is in the Old Testament, with 334 occurrences. [parenthetical note: these are the numbers on the computer search, Joseph L. Allen gives the numbers as 1,381 times in the Book of Mormon and 526 in the Old Testament (Exploring the Lands of the Book of Mormon, p. 31-32)] Why does it appear so often? So often, in fact, that Mark Twain once noted that the Book of Mormon would only be half it size were those words to be removed?
"And it came to pass" is a conjunctive phrase used in historical contexts. It functions to link sequential data somewhat analogous to my daughter's "and then she goes....". It is entirely possible that the linguistic unit which served that function on the plates could have been a single word or character. With the stated difficulty of writing on the plates, a long phrase would likely not have been used unless it held particular meaning. With the formulaic and structural function of "and it came to pass" it is more likely that it was easy to represent, and therefore used frequently.
One of the interesting points about the frequency of the phrase in the Book of Mormon is its comparison to the Old Testament, which is the next highest frequency of the phrase. One of the likely reasons for the numerical difference between the two is that the Old Testament contains a multiplicity to types of accounts, ranging from the poetic to the historical. As a phrase used to mark historical time and events, it would not be surprising to have it absent in poetic texts. It would be an interesting comparison to note the frequency of its occurrence in the Old Testament historical material. The suspicion is that the frequency would be higher, though even then perhaps not as high as the Book of Mormon.
As a curiosity, one of the Maya glyphs has been glossed with a similar function to "and it came to pass" (see Allen, Exploring the Lands of the Book of Mormon, p. 32). In fact, that would not be a forced reading of the function of the glyph. By the nature of Maya phonetic glyphs, the glyph is composed of multiple parts represented as a single unit. While the forms from the monuments are always complex (and frequently quite artistic) the corresponding forms on the painted codices show a reduction in detail. The monumental glyphs are elaborate, and the painted ones quicker outlines. In this particular case, the "and it came to pass" used in Maya writing would function as hypothesized for the Book of Mormon term on the plates, a historical linker which can be represented with a single graphic/word.