“In that day when the Lord shall come he shall reveal all things—things which have passed, and hidden things which no man knew” (D&C 101:32–33). “God shall give unto you knowledge by his Holy Spirit … that has not been revealed since the world was until now; which our forefathers have awaited with anxious expectation to be revealed in the last times, … a time to come in the which nothing shall be withheld” (D&C 121:26–28; see vv. 28–32 for details of great truths to be revealed).
The revelations of all dispensations will be restored in the millennial era, “and Satan shall have power over the hearts of the children of men no more, for a long time.” For reasons why Satan will have no power during the Millennium, see commentary at 1 Nephi 22:24–28.