D&C 42

As a portion of His law, the Savior revealed -

"...the elders, priests and teachers of this church shall teach the principles of my gospel, which are in the Bible and the Book of Mormon, in the which is the fulness of the gospel.
13 And they shall observe the covenants and church articles to do them, and these shall be their teachings, as they shall be directed by the Spirit."  (Doctrine and Covenants Section 42:12 - 13)

Herein, the Lord said that it is His law that if we are called to teach, we teach out of the scriptures and Church articles, and also the covenants.  But not only rely upon these doctrines but do it as directed by the Spirit for -

"...if ye receive not the Spirit ye shall not teach."  (Doctrine and Covenants
Section 42:14)
 
How does one receive the Spirit in teaching? 
 
"...the Spirit shall be given unto you by the prayer of faith..."  (Doctrine and Covenants
Section 42:14)
 
This simple doctrine suggests that we prepare to teach out of the "best books" in  sincere and faithful prayer.  The promise seems to be that if we follow this counsel, we will be directed by the Spirit in our teaching.  President Spencer W. Kimball taught -
 
"Apparently there were in the early Church those who taught for doctrines the sophistries of men. There are those today who seem to take pride in disagreeing with the orthodox teachings of the Church and who present their own opinions which are at variance with the revealed truth. Some may be partially innocent in the matter; others are feeding their own egotism; and some seem to be deliberate. Men may think as they please, but they have no right to impose upon others their unorthodox views. Such persons should realize that their own souls are in jeopardy. The Lord said to us through the Prophet Joseph Smith: [Sec. 42:12-14, quoted.]


The great objective of all our work is to build character and increase faith in the lives of those whom we serve. If one cannot accept and teach the program of the Church in an orthodox way without reservations, he should not teach. It would be the part of honor to resign his position. Not only would he be dishonest and deceitful, but he is also actually under condemnation, for the Savior said that it were better that a millstone were hanged about his neck and he be cast into the sea than that he should lead astray doctrinally or betray the cause or give offense, destroying the faith of one of 'those little ones' who believe in him. And remember that this means not only the small children; it includes even adults who believe and trust in God. . . .

In our own society, the murderer who kills the body is hunted, imprisoned, and executed, but the character who kills the soul by implanting doubt and shattering faith is permitted not only to go free but also is often retained in high places. The body which is killed will rise again in the resurrection with little damage to its eternal welfare, but he whose faith has been shattered may suffer long ages before complete restoration of spiritual stature can be had, if at all." (Spencer W. Kimball, CR, April 1948, p. 109.)

I recently read an article where a institute teacher did just that by voicing his personal opinion causing one to question and leave the Church.