Helaman 9:4

And now behold, when they saw this, they were astonished exceedingly, insomuch that they fell to the earth; for they had not believed the words which Nephi had spoken concerning the Chief Judge;

When they saw this, they were so amazed that they fell to the ground. They had not believed Nephi’s words about the chief judge.

The sight stunned them so completely that they collapsed to the ground. They hadn’t believed Nephi’s words about the Chief Judge at all.