2 Nephi 30:15 explains that "the earth shall be full of the knowledge of the Lord." What is it about the knowledge of the Lord that will create this peace and harmony? The next few verses begin to answer this question.
"The things of all nations shall be made known; yea, all things shall be made known unto the children of men. 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. 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" (2 Nephi 30:16-18).
When I think of secrecy I think of mistrust, miscommunication, misunderstanding, and unsurety. Because all things will be made known in the Millennium, all these negative effects of secrecy will disappear.
I imagine being in a classroom learning new material and not understanding that material. My peers get together to study together, but they don't allow me to join. They are secretive about it, because they want to have an unfair advantage over the rest of the class. This would leave me feeling mistreated, lost, and frustrated. If I didn't understand the material I would not have the ability to do well in the class. However, with knowledge, I would be enabled to pass the class and continue to receive further knowledge. I would feel fulfilled and liberated.
It is a beautiful prophecy that in the times preceding the Second Coming of Jesus Christ, "wisdom and knowledge shall be the stability of [our] times, and strength of salvation" (Isaiah 33:6).
In October 2013 general conference, President Dieter F. Uchtdorf said, "When the entire truth is eventually known, things that didn’t make sense to us before will be resolved to our satisfaction." All of us have questions, some of which will never be answered until we pass on to the next life. But letting those questions cause doubts lead us to stop progressing and gaining more knowledge. President Uchtorf says to "doubt your doubts before you doubt your faith. We must never allow doubt to hold us prisoner and keep us from the divine love, peace, and gifts that come through faith in the Lord Jesus Christ" (Dieter F. Uchtorf, "Come Join with Us").
It was necessary for Adam and Eve to exercise their faith in Jesus Christ after they chose to partake of the forbidden fruit. They were commanded not to partake of the fruit of the tree of knowledge of good and evil. They were given a choice, and they chose to eat the fruit. With their choice came the ability for Satan to tempt and try God's children. Because of this, it was necessary for God to provide a Savior to redeem all mankind from the results of the Fall. Without gaining knowledge, Adam and Eve would never have had the opportunity to progress and become like God. They would never experience good and evil and understand the difference. They would never have the opportunity to exercise their agency. They would never experience true joy. (See 2 Nephi 2:22-23.)
The Bible Dictionary states that "knowledge of divine and spiritual things is absolutely essential for one's salvation. . . . The scriptures, and also living prophets, are given so that the people might have knowledge of things of God. . . . Knowledge is one of the endowments of the Holy Ghost and one of the gifts of the Spirit. . . . Since no one can be saved in ignorance of the gospel, and one progresses only as fast as he gains knowledge, it follows that the person who gains knowledge will have 'the advantage in the world to come' (D&C 130:18-19)."
Knowledge comes from the Spirit of God which is the Spirit of peace. The Spirit gives us knowledge "and power according to [our] faith and desires which are in God" (Alma 18:35). When we receive knowledge through the Spirit, we discover the mysteries of God and "all the riches of the full assurance of understanding" (see Colossians 2:2-3).
In Romans 15, Paul lays out the beauty of obtaining knowledge from the scriptures: "For whatsoever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope. . . . Now the God of hope fill you with all joy and peace in believing, that ye may abound in hope, through the power of the Holy Ghost. And I myself also am persuaded of you, my brethren, that ye also are full of goodness, filled with all knowledge, able also to admonish one another" (Romans 15:4, 13-14). With knowledge we can obtain hope, joy, and peace, because we understand what is good.
As stated in the scriptures, the knowledge of the Lord will fill the earth before the Second Coming of the Savior. "And this is according to the prophecy, that they shall again be brought to the true knowledge, which is the knowledge of their Redeemer, and their great and true shepherd, and be numbered among his sheep" (Helaman 15:13).