D&C 50

As the Prophet Joseph Smith returned to Kirtland, he as well as other priesthood leaders found weird spiritual actions and influences being demonstrated by some of the saints.  After inquiring of the Lord, he was instructed -

"...that there are many spirits which are false spirits, which have gone forth in the earth, deceiving the world.
3 And also Satan hath sought to deceive you, that he might overthrow you."  (Doctrine and Covenants | Section 50:2 - 3)

For John also learned -

"For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world..."  (New Testament | Revelation 16:14)

It was under these conditions that the Lord said -

"...unto the elders of his church, and let us reason together, that ye may understand;
11 Let us reason even as a man reasoneth one with another face to face.
12 Now, when a man reasoneth he is understood of man, because he reasoneth as a man; even so will I, the Lord, reason with you that you may understand.  (Doctrine and Covenants | Section 50:10 - 12)

And in His reasoning, the Lord asked a series of questions, and then answered those questions -

"...unto what were ye ordained?
14 To preach my gospel by the Spirit, even the Comforter which was sent forth to teach the truth."  (Doctrine and Covenants | Section 50:13 - 14)

I specifically note that the Spirit is the Comforter which would suggest that as He teaches and testifies of truth, He does so with comfort, peace, assurance, joy, and understanding for when -

"...received ye spirits which ye could not understand, and received them to be of God; and in this are ye justified?
16 Behold ye shall answer this question yourselves; nevertheless, I will be merciful unto you; he that is weak among you hereafter shall be made strong."  (Doctrine and Covenants | Section 50:15 - 16)

For -

"...he that is ordained of me and sent forth to preach the word of truth by the Comforter, in the Spirit of truth, doth he preach it by the Spirit of truth or some other way?
18 And if it be by some other way it is not of God."  (Doctrine and Covenants | Section 50:17 - 18)

Sometimes we see people trying to teach the truth or untruths in "flattering" or emotional ways.  This should not be interpreted as the Spirit.  We see many teaching with flattering words in the Book of Mormon...Sherem, Nehor, and Korihor.

And again, he that receiveth the word of truth, doth he receive it by the Spirit of truth or some other way?
20 If it be some other way it is not of God."  (Doctrine and Covenants | Section 50:19 - 20)

The Lord summarizes -

Therefore, why is it that ye cannot understand and know, that he that receiveth the word by the Spirit of truth receiveth it as it is preached by the Spirit of truth?
22 Wherefore, he that preacheth and he that receiveth, understand one another, and both are edified and rejoice together."  (Doctrine and Covenants | Section 50:21 - 22)

And as He reasons, He provides this clear doctrine on how we may progress or limit our progression -

"that which doth not edify is not of God, and is darkness.
24 That which is of God is light; and he that receiveth light, and continueth in God, receiveth more light; and that light groweth brighter and brighter until the perfect day.
25 And again, verily I say unto you, and I say it that you may know the truth, that you may chase darkness from among you..."  (Doctrine and Covenants | Section 50:23 - 25)