D&C 67

 As some pious brethren thought that they could write a revelation as well as Joseph Smith, the Lord challenges them - 

"Now, seek ye out of the Book of Commandments, even the least that is among them, and appoint him that is the most wise among you;

7 Or, if there be any among you that shall make one like unto it, then ye are justified in saying that ye do not know that they are true;

8 But if ye cannot make one like unto it, ye are under condemnation if ye do not bear record that they are true.

9 For ye know that there is no unrighteousness in them, and that which is righteous cometh down from above, from the Father of lights."  (Doctrine and Covenants 67:6–9)

We come to realize that it these revelations are not just the words, but come with the Spirit of the Holy Ghost for the Lord adds - 

"...a promise I give unto you that have been ordained unto this ministry, that inasmuch as you strip yourselves from jealousies and fears, and humble yourselves before me, for ye are not sufficiently humble, the veil shall be rent and you shall see me and know that I am—not with the carnal neither natural mind, but with the spiritual.

11 For no man has seen God at any time in the flesh, except quickened by the Spirit of God."  (Doctrine and Covenants 67:10–11)

The testimony of the word of Christ cometh from the Holy Ghost.