Three times a year under the Law of Moses, men, women, and children had to come to the temple. These were festival days, such as the Feast of Tabernacles, and they were filled with feasting, rejoicing, celebration, glorifying God, being grateful for the giving of the law, and the performing of sacrifices to atone for all sins. Even the Day of Atonement—which begins with fasting, prayer, and mourning—ends with a great time of jubilation as the people rejoice about how they have been blessed. It also may have been the coronation of the second Nephite king. So it was likely a big event with a big gathering, and may have had multiple sessions. Despite the many activities going on, Jacob’s sermon was possibly the first order of business. And it seems to me that the people might have been a little surprised at what he told them.
According to Deuteronomy 31:9–13, the Levitical priests were required to read the law so that the people could hear the word of the Lord. They were to be taught the same thing over and over, much like we are today. But there is also here a sense that this is sort of General Conference, and that Jacob was inspired to deliver a particular message to the people, based on their needs. Jacob declared in the previous chapter that before giving his speech, he "first obtained [his] errand from the Lord" (Jacob 1:17). I can’t imagine him having the courage to address such difficult topics without the Lord’s mandate. King Benjamin essentially says the same thing in his speech, declaring that "the things which I shall tell you are made known unto me by an angel from God" (Mosiah 3:2). So, in both cases, these prophets emphasize that their message is indeed the word of the Lord, even though it may not have been a rote presentation of the law.