(Isa. 8:20; 2 Ne. 12:5)
There are two great scriptural tests which show whether men have the light and are walking therein, one pertaining to beliefs, the other to conduct. Isaiah challenged false teachers with this test: “To the law and to the testimony: if they speak not according to this word, it is because there is no light in them” (Isa. 8:20). And John, speaking particularly to members of the Church, those upon whom “the true light now shineth,” said: “He that saith he is in the light, and hateth his brother, is in darkness even until now. He that loveth his brother abideth in the light, and there is none occasion of stumbling in him. But he that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes” (1 Jn. 2:8–11).
(Bruce R. McConkie, Mormon Doctrine, 2d ed. [Salt Lake City: Bookcraft, 1966], 445–46.)
May I suggest three short tests to avoid being deceived… .
1. What do the standard works have to say about it? “To the law and to the testimony: if they speak not according to this word, it is because there is no light in them,” said Isaiah (Isa. 8:20). This is one of the great truths of Isaiah so important that it was included in the Book of Mormon scriptures… .
2. The second guide is: what do the latter-day Presidents of the Church have to say on the subject—particularly the living President? …
3. The third and final test is the Holy Ghost—the test of the Spirit. By that Spirit we “… may know the truth of all things” (Moro. 10:5).
(Ezra Taft Benson, Conference Report, Oct. 1963, 16–17.)
To those in quest of spiritual light—this word of counsel: Seek it only in God’s appointed way. Follow the advice of the Apostle James and the example of Joseph the Prophet. (James 1:5; Hist. Ch. vol.1, 4, 5.) Never go upon the Devil’s ground. Keep away from all deceptive influence. One may believe in hypnotism, without being a hypnotist, without surrendering one’s will to the will of the person exercising that power—a very dangerous power when wielded by an unprincipled possessor. In like manner, one may believe spiritualism real, without becoming a spiritualist, without attending “seances,” without consulting “mediums,” without putting trust in planchettes, ouija boards, automatic pencils, false impersonations, etc., or in any way encouraging the advances of designing spirits, who thus gain an ascendancy over their victims, leading them into mazes of delusion, and often into depths of despair. Go not after them; and if they come to you, put them to the test “Try the spirits” (1 Jn. 4:1). If they speak not according to revealed truth,—if they conform not to divine standards, “it is because there is no light in them” (Isa. 8:20).
(Orson F. Whitney, Saturday Night Thoughts [Salt Lake City: The Deseret News, 1921], 312.)