In speaking to Zeezrom and the people of Ammonihah (who were apparently of Mulekite descent--see Alma 8:20), Alma perceived that Amulek had caught Zeezrom in his lying and deceiving to destroy him,
and seeing that he began to tremble under a consciousness of his guilt, he opened his mouth and began to speak unto them, and to establish the words of Amulek, and to explain things beyond, or to unfold the scriptures beyond that which Amulek had done. Now the words that Alma spake unto Zeezrom were … on this wise: Now Zeezrom, seeing that thou hast been taken in thy lying and craftiness, for thou has not lied unto men only but thou hast lied unto God; for behold, he knows all thy thoughts, and thou seest that thy thoughts are made known unto us by his Spirit … they that will harden their hearts, to them is given the lesser portion of the word until they know nothing concerning his mysteries; and then they are taken captive by the devil, and by his will down to destruction… . For our words will condemn us, yea, … and our thoughts will also condemn us … (Alma 12:1-3, 11, 14)
It is significant that Alma testified to Zeezrom that “our thoughts will also condemn us,” for John Tvedtnes links this concept of being judged for one’s thoughts with something that Jesus said to the Jews in his Sermon on the Mount. In that sermon Jesus said, “Think not that I am come to destroy the law or the prophets. I am not come to destroy but to fulfil” (Matthew 5:17; 3 Nephi 12:17). According to Tvedtnes, in order to fully understand this statement, we must begin by examining the law of Moses [and the history of Israel as it applies to the Nephites and Lamanites in type and shadow].
Appearing to Moses in the Sinai wilderness, the Lord said, “When thou hast brought forth the people out of Egypt, ye shall serve God upon this mountain” (Exodus 3:12). When the children of Israel had assembled at the base of the mountain, the Lord promised, “If ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people… . And ye shall be unto me a kingdom of priests, and an holy nation” (Exodus 19:5, 6).
In the end, however, only a few of the Israelite leaders were allowed to go atop the mountain to see God (Exodus 24:9-11 … The reason for this change is found in the intervening events. Immediately after the Lord recited the Ten Commandments to all Israel:
all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking: and when the people saw it, they removed and stood afar off. And they said unto Moses, Speak thou with us, and we will hear: but let not God speak with us, lest we die (Exodus 20:18-19).
That report indicates the people’s unwillingness to communicate directly with God and their desire to have Moses be their intermediary. By so doing, they rejected the responsibility of being a “kingdom of priests.” Joseph Smith explained that “God cursed the children of Israel because they would not receive the last law from Moses… . The Israelites prayed that God would speak to Moses and not to them; in consequence of which he cursed them with a carnal law” (History of the Church, 5:555). In so doing, they were rejecting the higher priesthood, which holds the keys of communing directly with God (D&C 107:18-19), and consequently did not become the “kingdom of priests” God intended them to be. (See also D&C 84:21-26.) … Brigham Young explained the situation thus:
"If [the children of Israel] had been sanctified and holy, they would not have travelled one year with Moses before they would have received their endowments and the Melchizedek Priesthood. But they could not receive them, and never did. Moses left them and they did not receive the fulness of that Priesthood. After they came to the land of Canaan, THEY NEVER WOULD HAVE DESIRED A KING, had they been holy. (Journal of Discourses, 6:100, emphasis added).
The seventh chapter of Hebrews notes that, with the coming of Christ as a high priest after the order of Melchizedek, there was necessarily a change in the law. [But compare the tone of Alma 13 which touches on the same subject matter] The prophet Jeremiah recorded the Lord’s promise of a “new covenant” that was to replace the covenant made in the days of Moses. This new law would be placed in the people’s hearts and they would all have direct access to the Lord, along with forgiveness of sins (Jeremiah 31:31-34).
Hebrews 8:7-13 and 10:16-20 cite the Jeremiah 31 passage as evidence that the covenant of Moses was to be replaced by a higher covenant under Christ. For this reason, the early Christians saw themselves as the chosen of God in the place of Israel, leading Peter to paraphrase the Lord’s original promise at Sinai (Exodus 19:6), saying, “But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people” (1 Peter 2:9).
To the Jews in the Sermon on the Mount [and also to the Nephites in the Sermon at the Temple], Christ said that he was not “come to destroy the law, or the prophets … but to fulfil” (Matthew 5:17; 3 Nephi 12:17), and he reiterated the need to keep the commandments (Matthew 5:19-20; 3 Nephi 12:19-20). He then proceeded to explain the difference between the law of Moses and the higher law that he was establishing. Whereas the law of Moses commanded not to kill (Exodus 20:13), Christ teaches that we should not be angry (Matthew 5:21-22; 3 Nephi 12:21-22). The law of Moses forbade adultery (Exodus 20:14), but Christ tells us not to lust in our hearts (Matthew 5:27-28; 3 Nephi 12:27-28).
Thus, while the higher law condemns sinful acts, its real emphasis is on the thoughts that engender those acts. This is what is meant by the law’s being written in our hearts instead of on tablets of stone, as in the days of Moses (see Jeremiah 31:33; Isaiah 51:7; Proverbs 3:3; Ezekiel 11:19-20; 2 Corinthians 3:3). It may also explain what the Prophet Joseph Smith meant when he said that the Israelites “would not receive the last law from Moses,” if he was referring to the last of the Ten Commandments, “Thou shalt not covet” (Exodus 20:17). This was the one commandment for which one could not be punished under the law of Moses, since it would be impossible to find witnesses who could testify about the thoughts and intents of another person. Under the higher law, God judges us not only on the basis of our outward actions and words, but also by taking into account even our thoughts (Mosiah 4:30; Alma 12:14). [John A. Tvedtnes, “The Sermon on the Mount: Restoration of the Higher Law,” in Insights, F.A.R.M.S., February 1999, pp. 4-5]