At this point, a little over halfway through his speech, when King Benjamin looked around, he found that his people had all fallen "to the earth." There was a big crowd, and we may wonder why they all had responded with the same physical response and all at the same time. The text says that the fear of the Lord had come upon them. The word for "to fear" and the word for “to revere” are related. In this context, the people’s fear most likely refers to a deep, powerful reverence for God, as when someone is a God-fearing person. Of course, the fear may also have been connected with the power that they knew the Lord had to administer eternal justice. They could also have been afraid because of their inadequacies and the seriousness of the covenant into which they knew they would soon be entering.
In Jerusalem, on the Day of Atonement, when the people heard the sacred name of the Lord pronounced by the High Priest, they fell down as if they were in the Lord’s sacred presence. Similarly, in Lehi’s dream, the people fall down when they reach the Tree of Life and partake of the fruit: "and they came and caught hold of the end of the rod of iron; and they did press their way forward, continually holding fast to the rod of iron, until they came forth and fell down and partook of the fruit of the tree" (1 Nephi 8:30). There were four groups of people that had worked their way to the Tree of Life. Three of the groups either do not make it or soon fall away. Those who stay faithful are the ones who fall down when they get there, and make themselves as humble as the earth. Talk about being humble! When we as modern people bow down, we typically just bow our heads, but the ancient people bowed their bodies. When they came into a divine situation or into the presence of a great ruler, like a king or emperor, they would prostrate themselves in front of that person.
Book of Mormon Central, "Why Did the People Fall Down at the Feet of Jesus? (3 Nephi 11:17)," KnoWhy 202 (October 5, 2016).