Jacob says, "For behold, as yet, ye have been obedient unto the word of the Lord, which I have given unto you" (Jacob 2:4). Apparently they were at least outwardly performing the ordinances of the temple, whatever those were. But then Jacob follows up this statement by declaring, "But behold, hearken ye unto me, and know that by the help of the all-powerful Creator of heaven and earth I can tell you concerning your thoughts, how that ye are beginning to labor in sin, which sin appeareth very abominable unto me, yea, and abominable unto God" (Jacob 2:5).
Over and over again, the authors of these small plates tell us that the Nephites were strict in observing the Law of Moses, and several centuries later, at this same temple, King Noah will perform daily sacrifices. Yet, speaking to Noah and his priests, Abinadi basically said, "You do this, you go through the motions, but you’re just doing it mechanically; you don’t understand what it’s all about, and you’re not doing it righteously." It is possible that the people in Jacob’s day had similarly misunderstood the meaning of the ordinances set forth in the Law of Moses. The daily sacrifices at the temple would have been the thank offerings of bread and of grain, and there are a number of those. There were also atonement sacrifices. If people had committed a sin of some kind, they needed to bring an atonement sacrifice and, of course, those are symbols of the Atonement of Jesus Christ. Nephite prophets understood that the Law of Moses just looks forward to the great sacrifice that will come (Mosiah 13:27–28). But the people generally were prone to obey the outward ordinances but fail to live up to the other commandments and standards of the Lord.
Jacob’s language indicates that this is just a preliminary happening—the people are only now just "beginning to labor in sin" (Jacob 2:5). And he indicates that he only knows the extent of this problem because the Lord is revealing it to him. So there is an element of prophecy here. On several occasions in chapter 2, Jacob says that he is absolutely obligated to address this issue—he must tell them of their wickedness. He says:
The first one is interesting because Jacob focuses on the wickedness of their "hearts." There are several other occasions during the speech where he similarly emphasizes thoughts and intentions. So it is clearly more than just their doings. I think most of us have experienced that nanosecond when we know something is not right, and we are left to choose what to think or how to act, knowing fairly clearly which path will lead away from God. In some cases, the warnings from the Spirit are much more than a nanosecond; they provide a very clear and sustained understanding that something is wrong. It is by entertaining sinful thoughts and desires in our hearts that the seeds of disobedient or rebellious actions are planted within us.