In 3 Nephi 18:2, Jesus commanded the people that they “should sit.” Why did the Book of Mormon scribes bother to record and tell us that these people were all asked to sit? Is every word in the Book of Mormon there for a purpose? Presumptively, yes, and perhaps even for multiple purposes.
First, Jesus was concerned for their comfort. The multitude had probably been standing for a long time. In chapter 17, the children had been blessed, and the multitude had stood, then knelt, then stood again. The nature of the Savior is such that when people had been kneeling for a prayer for some time, he asked them to rise; when they were tired, he asked them to sit; and when they were hungry, he and his ministering angels provided spiritual and physical food. He was very aware of the needs of the people.
Second, Jesus asked them to sit to put themselves in a position to truly receive the sacrament. Latter-day Saints sit as the sacrament is blessed and passed to the congregation. Some churches have the congregation stand to take the sacrament, and some kneel, often at an altar. One may ask what difference any of that makes. Is there symbolism in being asked to “sit”? When people stand in a group, they are either waiting to be told what to do or watching something happening. People are invited to sit when they are about to be taught, and indeed partaking of the sacrament is a time to be taught. The Nephite multitude needed to be in a situation not only to be taught what they needed to know, but also to learn by the spirit of what they needed to repent.
Third, it was polite for them to wait upon the Lord. In many cultures and literatures, one must be invited to sit. Until then, humble servants stand ready and at attention. Isaiah saw that in the messianic day, Jerusalem would be invited to arise, come forth, and “sit down” (Isaiah 52:2; 2 Nephi 8:25). Alma promised the righteous that they would “sit down in the kingdom of God” (Alma 5:24; 29:17; see also Alma 34:36; 28:15; 3 Nephi 28:10). But kings were seated, and the exalted will “sit down with Abraham, Isaac, and Jacob” (Alma 7:25; Helaman 3:30). Seats were designated for chief judges and priests (Alma 50:40; Mosiah 11:11). Jesus Christ himself “sitteth on the right hand” of God the Father in his power (Moroni 9:26). Sitting, especially in the presence of God, is not something casual.
Fourth, in this connection, the sacrament is also connected to the Passover meal, as it was for the Last Supper in Jerusalem. Not only are certain honors involved in being seated, but also having passed successfully through a certain degree of vulnerability. The Israelites had been through a series of terrible events in Egypt. Being seated at the Passover, protected by the blood of the Lamb, was an indication of now being safe and connected as a family and people. It signified that life was now more stable. Being seated for the Nephites may have been reminiscent of being seated at their Passover Seder and now with the Savior Himself.