Alma and Benjamin both state we shall be judged of our words, our works, and our thoughts. (Alma 12:14; Mosiah 4:30.) Elsewhere in the Book of Mormon it is made clear that we shall also be judged of our responsibilities concerning the welfare of others. (Jacob 1:18-19; Mosiah 2:20-28, 36-41; Mosiah 4:19-30.) Perhaps the most difficult area of judgment for people to understand is that which deals with our thoughts. Yet the Savior very clearly taught that we shall be responsible for what we think (Matthew 5:27-28), and this truth has also been taught by other prophets (1 Chronicles 28:9; Job 42:2; Psalm 94:11; Romans 2:16). The following statements by two of the Presidents of the Church in this dispensation are interesting in this regard:
In reality a man cannot forget anything. He may have a lapse of memory; he may not be able to recall at the moment a thing that he knows or words that he has spoken; he may not have the power at his will to call up these events and words; but let God Almighty touch the mainspring of the memory and awaken recollection, and you will find then that you have not even forgotten a single idle word that you have spoken! I believe the word of God to be true, and, therefore, I warn the youth of Zion, as well as those who are advanced in years, to beware of saying wicked things, of speaking evil, and taking in vain the name of sacred things and sacred beings. Guard your words, that you may not offend even man, much less offend God. (Joseph F. Smith, quoted in Latter-day Prophets Speak [Bookcraft, 1948], pp. 56-57.)We read something like this, “But I say unto you, that every idle word that men shall speak, they shall give account thereof in the day of judgment.” Now, this is a remarkable declaration… . God has made each man a register within himself, and each man can read his own register, so far as he enjoys his perfect faculties. This can be easily comprehended.
Let your memories run back, and you can remember the time when you did a good action, you can remember the time when you did a bad action; the thing is printed there, and you can bring it out and gaze upon it whenever you please… . Where do you read all this? In your own book. You do not go to somebody else’s book or library, it is written in your own record, and you there read it. Your eyes and ears have taken it in, and your hands have touched it; and then your judgment, as it is called, has acted upon it—your reflective powers. Now, if you are in possession of a spirit or intellectuality of that kind, whereby you are enabled to read your acts, do you not think that that being who has placed that spirit and that intelligence within you holds the keys of that intelligence, and can read it whenever he pleases? Is not that philosophical, reasonable, and scriptural? I think it is… . Well, then, upon this principle we can readily perceive how the Lord will bring into judgment the actions of men when he shall call them forth at the last day. (John Taylor, Journal of Discourses, 11:77-78.)
If I had time to enter into this subject alone, I could show you upon scientific principles that man himself is a self-registering machine, his eyes, his ears, his nose, the touch, the taste, and all the various senses of the body are so many media whereby man lays up for himself a record which perhaps nobody else is acquainted with but himself; and when the time comes for that record to be unfolded all men that have eyes to see, and ears to hear will be able to read all things as God Himself reads them and comprehends them, and all things, we are told, are naked and open before Him with whom we have to do. (John Taylor, quoted in Latter-day Prophets Speak, p. 57.)
The Book of Mormon clearly teaches that God knows our thoughts (Alma 18:32) and that we shall be held responsible for them.