16 Wherefore, the things of all nations shall be made known; yea, all things shall be made known unto the children of men.
17 There is nothing which is secret save it shall be revealed; there is no work of darkness save it shall be made manifest in the light; and there is nothing which is sealed upon the earth save it shall be loosed.
18 Wherefore, all things which have been revealed unto the children of men shall at that day be revealed; and Satan shall have power over the hearts of the children of men no more, for a long time.
That everything men keep secret will be revealed is a promise God makes repeatedly in the scriptures. Everyone has secrets that they keep, afraid to reveal to others. The idea that those things might be shouted from the housetops is unnerving. However, the Savior saved His harshest words for pretenders and hypocrites, calling them "whited sepulchers" that look good on the outside but are full of ruin inside.
Keeping those secret sins is a tremendous burden in some lives. I have counseled people who put on a righteous face, but in private are bound with sin and are terrified of being found out by a spouse or their children or their parents. Proverbs 28: 13 says
13 He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.
Verse 18 in this chapter of 2 Nephi suggests that all things that God has revealed to men on the earth will be revealed in the last days. Verse 15 repeats the Lord's promise found elsewhere that the earth will be full of the knowledge of the Lord as the waters cover the sea. Knowledge of all things revealed is the key to freedom from sin and error. That knowledge, properly applied, will bind Satan as he will have no power over us.