The unmistakable signs in the heavens will cause all to “fall to the earth.” That concept is used frequently to represent being overcome with the Spirit, or to otherwise be overwhelmed. We have seen it in the stories of Alma the Younger, Lamoni and his wife, and then Lamoni’s father. All fell to the earth when overcome by the spirit. That is the allusion in verse 7.
These signs are witnesses to the truth of the preaching of the Messiah that has been the fundamental Nephite religious belief from the first Nephi’s time. The signs will not cause belief, but for those who do recognize the import of the signs and “believe on the Son of God, the same shall have everlasting life.”