D&C 50 - 52

Speaking of Satan, the Savior said that he "...abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
(New Testament John 8:44)

Mormon said the same of Satan's followers -
"...whatsoever thing persuadeth men to do evil, and believe not in Christ, and deny him, and serve not God, then ye may know with a perfect knowledge it is of the devil; for after this manner doth the devil work, for he persuadeth no man to do good, no, not one; neither do his angels; neither do they who subject themselves unto him.
(Book of Mormon Moroni 7:17)

In the early days of the Church, truth was revealed "...precept upon precept; line upon line, line upon line; here a little, and there a little..."(Old Testament Isaiah 28:10). The Lord warned the saints that in opposition "...there are many spirits which are false aspirits, 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)

Even amongst the saints, he warned "...I, the Lord, have looked upon you, and have seen abominations in the church that profess my name. " (Doctrine and Covenants Section 50:4) "...verily I say unto you, there are hypocrites among you, who have deceived some, which has given the adversary power;"(Doctrine and Covenants Section 50:7) "Wherefore, let every man beware lest he do that which is not in truth and righteousness before me." (Doctrine and Covenants Section 50:9)

The Savior then guides us in not being deceived -

"...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.
19 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.
21 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.
23 And that which doth not edify is not of God, and is darkness.
(Doctrine and Covenants Section 50:17 - 23)

Or in other words, darkness is the deceptions of Satan, For "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." (Doctrine and Covenants Section 50:24)

"...And if ye are purified and cleansed from all sin, ye shall ask whatsoever you will in the name of Jesus and it shall be done.
30 But know this, it shall be given you what you shall ask[see D&C 46:28,30]; and as ye are appointed to the head, the spirits shall be subject unto you.
(Doctrine and Covenants Section 50:29 - 30)

:...for Satan desireth to sift [you] as chaff."(Doctrine and Covenants Section 52:12). But "...I will give unto you a pattern in all things, that ye may not be deceived;"(Doctrine and Covenants Section 52:14) For "...he that prayeth, whose spirit is contrite, the same is accepted of me if he obey mine cordinances." For "...he that speaketh, whose spirit is contrite, whose language is meek and edifieth, the same is of God if he obey mine ordinances. (Doctrine and Covenants Section 52:15 - 16)

As we follow these divine directives, we will not be deceived.