It is through revelation that we can gain a testimony of Jesus Christ. Peter could testify that Jesus was the Christ because of revelation, Matthew 16:15-17. The Father is revealed through the Son and the Father and the Son are one, Matthew 11:27, JST. Matthew 11:27-28, Luke 10:22, and JST Luke 10:22-23. The gospel doesn't come from men, but from Jesus Christ, Galatians 1:11-12. We are not given knowledge about the gospel all at once, but instead are given line upon line, 2 Nephi 28:30.
The Holy Ghost is a revelator. In the Bible Dictionary page 762 a quote from Joseph Smith says "no man can receive the Holy Ghost without receiving revelations." The Holy Ghost will reveal things to come, John 16:13, and show us all things that we should do, 2 Nephi 32:5. The Lord speaks by the voice of His Spirit, D&C 75:1. Zeezrom's thoughts are revealed to Alma and Amulek through the Holy Spirit, Alma 12:3. Those who are not stiffnecked and have faith communion with the Holy Spirit, Jarom 1:4. No man can see God except they are quickened by the Spirit, D&C 67:11. The things that Joseph Smith and Sidney Rigdon saw in section 76, the "vision," can only be understood by the power of the Holy Spirit, D&C 76:116. The Comforter testifies of Christ, John 15:26. The Lord sent the Apostles the Comforter who is the spirit of truth, John 14:15-17 and the Comforter would teach all things to the Apostles, John 14:25-26.
The Lord reveals his will to us through the scriptures. We hear the Lord's voice and know His words by reading the scriptures to each other, D&C 18:33-36. The scriptures are the word of God, D&C 27:1. The instruction and prophesies in the D&C will all be fulfilled, D&C 1:37-38. The promise of the Book of Mormon is that we can know the truth of it for ourselves, Moroni 10:4-5. Those that don't believe in continuing revelation don't understand the gospel of Christ or the scriptures, Mormon 9:7-8. If miracles cease it is because of last of faith in the people, Moroni 7:37. We do not live by bread alone but by every word that proceedeth from the mouth of God, Genesis 8:3, Matthew 4:4, and D&C 98:11. What is spoken when moved on by the Holy Ghost is scripture, D&C 68:3-4. If we harned our heart we receive the lesser part of the word, Alma 12:10-11.
Alma compares the word unto a seedAlma 32:28-33, but after the seed sprouth it still will not develop without care, Alma 32:37-41.
The Lord makes known unto just and holy men what will happen in the future, Amos 3:7. Throughout all ages the Lord speaks to man, Job 33:14. The scripture in Amos is the one we usually think of but there is also one in Alma Alma 13:26. God lets his prophets know what will happen in the future. The Lord revealed to Abraham the things that he would do on the earth (destroy Sodom), Genesis 18:17. The Lord shows Mormon what will happen when the Book of Mormon comes forth, Mormon 8:34. Joseph Smith was given instruction from heaven what was to come unto the world, D&C 1:17. Alma is guided by the spirit of revelation and prophecy, Alma 4:20. When Nephi and Lehi were imprisoned they beard a voice telling the people what they should do, Helaman 5:30-31. Joseph Smith and Sidney Rigdon are to teach the people and say what the Lord puts into their hearts, D&C 100:5-6. Patriarch are to be chosen by revelation in "large branches" of the Church, D&C 107:39.
Joseph tells the chief butler and chief baker that it is God that can interprets dreams, Genesis 40:8. Similarly he tells Pharaoh that it not him that interprets dreams but is God through him, Genesis 41:15-16, because he has the Spirit of God with him, Genesis 41:37. By the knowledge of God Daniel is able to interpret Nebuchadnezzar's dream and tell the king what will happen in the future, Daniel 2:45.
While Jesus was on the earth he taught his disciples all that they would need to know. The Lord called his apostles friends and tells them he will make all things know unto them, John 15:15. Jesus teaches the apostles the things that the Father gave unto Him to teach, John 17:8. The apostles saw Moses and Elias and heard the voice of the Father on the mount of transfiguration, Matthew 17:2-5, Mark 9:2-7, Luke 9:28-35 and, 2 Peter 1:18.
In scriptures there are many examples of the Lord speaking directly to his prophets and leaders. When Joseph Smith went into the woods to pray the Father and the Son appeared to him, Joseph Smith History 1:15. The scripture that inspired Joseph Smith to go into the woods to pray, James 1:5-7. The Lord spoke directly to Samuel when he was a still a young boy, Samuel 3:3-10. Joseph F. Smith had a vision where he saw the spirit world, D&C 138:11. The Lord spoke to Elijah, 1 Kings 19:9. God showed unto Elijah his power, but he spoke in a still small voice, 1 Kings 19:11-13. The voice of the Lord spoke to Lehi, 1 Nephi 16:9. Nephi is told by the Spirit to kill Laban, 1 Nephi 4:18. Enos prayed to the Lord and the Lord answered him, Enos 1:4. It is interesting to note that the voice that Enos heard was in his mind, Enos 1:10. Paul is guided by revelation, Galatians 2:2, and teaches by revelation, 1 Corinthians 14:6 and 2 Corinthians 12:1.
The Prophet is the only one that receives commandments for the whole Church, D&C 43:2-6. but we can receive revelation for our own dominion D&C 28:2-8, D&C 100:11, and D&C 107:91-92. The President of the Church is a seer and a revelator, D&C 107:91. The president of the church is appointed by revelation and acknowledged by the voice of the Church, D&C 102:9. The president of the Church gets revelation for the Church respecting doctrine or principle, D&C 102:23. Joseph Smith was called to reveal all things that the Lords wants revealed to the Church, D&C 25:9. Joseph is the presiding elder over the Church and is a revelator, a seer, and a prophet, D&C 124:125. Leaders of the Church can also be guided by the voice of the Spirit in temporal things D&C 104:36. Joseph Smith is to receive revelations "to unfold the mysteries of the kingdom;" D&C 90:14. All bonds, obligations, etc are of no power unless made by proper authority and sealed by the the Holy Spirit of Promise. There is only one person at a time that holds all the keys, D&C 132:6-7.
A number of prophets have seen a vision of everything that will happen on the earth. The Apostle John and the book of revelations is the one we usually think of, Revelation 4:1. The Book of Revelations is a revelation from Jesus Christ, Revelation 1:1. Enoch also saw the Lord and was shown what will happen on the earth in the future, Moses 7:4. He is shown all things that will happen on the earth, Moses 7:67. The sealed portion of the gold plates contains a revelation telling of the history of the world and what will happen in the future, 2 Nephi 27:7-8. The Lord showed the brother of Jared a vision where he saw all that had been and will be upon the earth, Ether 3:25. We are promised that some day these things will be made manifest, Ether 3:27. The day will come when all things will be revealed that have ever have been known among the children of men, 2 Nephi 27:11.
The Lord will reveal things to ordinary members as well as to the prophets. In the parable of the sheepfold we learn that the righteous know the Lord's voice, John 10:4. Paul prays that the Ephesians will have the spirit of wisdom and revelation, Ephesians 1:17. The Lord is the same yesterday, today, and forever and speaks to His people, 2 Nephi 29:9. The people that stand in Zion will be blessed with revelations, D&C 59:3-4. "Ask, and it shall be given you; seek, and ye shall find," Matthew 7:7-11 and 3 Nephi 13:7-11. The Lord will tell us the truth in our mind and in our heart, D&C 8:2-3. If we ask we can receive revelations, D&C 42:61. This scripture was probably directed to Joseph Smith, but it applies more generally.
We can receive revelations from God, but we need to do our part first. Alma knows the things of God are true because he has fasted and prayed many days, Alma 5:45-46. The same is true for the sons of Mosiah, Alma 17:2-3. We need to believe in revelation and the other spiritual gifts, Omni 1:25. "ye receive no witness until after the trial of your faith." Ether 12:6. "Deny not the spirit of revelation," D&C 11:25. We need to follow the revelation that we receive, D&C 82:3-4. Lyman Sherman is told through the prophet Joseph to resist no more the Lord's voice, D&C 108:2.
We need to be careful of boasting in our own strength, D&C 3:4. If we sanctify ourselves the Lord will reveal himself unto us in His on way and time, D&C 88:68. The Lord will manifest himself to those who love Him and keep His commandments, John 14:21. No "man hath seen the Father, save he which is of God," John 6:46. "Where there is no vision, the people perish," Proverbs 29:18. We need to do what we can on our own, then ask God, D&C 9:7-9.
In the funllness of times everything will be revealed, D&C 121:26-31. Some of these things have been revealed by science not revelation. We are also told that righteousness and truth will come to the New Jerusalem and fill the "earth as with a flood," Moses 7:62. Knowledge of the mysteries comes through revelation, Ephesians 3:3-5.
In a vision given to Joseph Smith the Lord told him that those who died without a knowledge of the gospel but would have received it if they would have had the chance are heirs of the celestial kingdom, D&C 137:7.