Mormon tells us he purposely did not record all the detail of the “blood and carnage” of those terrible years, this in order to prevent the latter-day reader from having an unnecessary and soul-troubling view of it all. His statement that all things “must be revealed” has a dual meaning.
Several scriptural passages testify that at the Judgment all deeds, words, thoughts, and intents of the heart-both righteous and wicked-will be revealed will be shouted from the housetops, as it were, for all to know (see Matthew 10:26-27; D&C 1:3; D&C 88:108-10).
Undoubtedly Mormon had this doctrinal concept in mind as he spoke of the wickedness of his own civilization, but examining the context of this statement leads one to believe that Mormon may have also been referring to another, more specific, way in which the fuller record of the Nephites would be revealed. In the next several verses we read of the knowledge of his people that will come forth because of his record. Throughout his record Mormon speaks of other records or accounts, even another set of plates, that contain additional information and a “more history part” of the peoples (see 2 Nephi 4:14).
Being familiar with the prophecies of those holy men who had preceded him, Mormon was probably also referring to the coming forth of those records that were sealed. As this record which is “sealed by the power of God” comes to light in the last days, all the workings of God will be revealed, and the deeds and destructions of the Nephites and the Lamanites which Mormon could not describe will indeed “be revealed upon the house-tops” (see 2 Nephi 27:10-11; see also Commentary 1:316-18).