D&C 33:10-13
10 ...Repent, repent, and prepare ye the way of the Lord, and make his paths straight; for the kingdom of heaven is at hand;
11 Yea, repent and be baptized, every one of you, for a remission of your sins; yea, be baptized even by water, and then cometh the baptism of fire and of the Holy Ghost.
12 Behold, verily, verily, I say unto you, this is my gospel; and remember that they shall have faith in me or they can in nowise be saved;
13 And upon this rock I will build my church; yea, upon this rock ye are built, and if ye continue, the gates of hell shall not prevail against you.
In the Book of Mormon, the gospel is also called the doctrine of Christ (Jacob 7:6). And it is the same throughout scripture.D&C 39:1-6
1 Hearken and listen to the voice of him who is from all eternity to all eternity, the Great I Am, even Jesus Christ—
2 The light and the life of the world; a light which shineth in darkness and the darkness comprehendeth it not;
3 The same which came in the meridian of time unto mine own, and mine own received me not;
4 But to as many as received me, gave I power to become my sons; and even so will I give unto as many as will receive me, power to become my sons.
5 And verily, verily, I say unto you, he that receiveth my gospel receiveth me; and he that receiveth not my gospel receiveth not me.
6 And this is my gospel—repentance and baptism by water, and then cometh the baptism of fire and the Holy Ghost, even the Comforter, which showeth all things, and teacheth the peaceable things of the kingdom.
The gospel is that men should 1. repent, 2. be baptized by water, 3. be baptized by fire and the Holy Ghost, which constitutes receiving the Holy Ghost (implicit in this is that one has faith in Jesus Christ [D&C 33:12, quoted at the top]). If these three things are done, then a person is on the path which leads to eternal life, in which path they must endure to the end. There is no other way spoken of in scripture.2 Nephi 31:17-21
17 Wherefore, do the things which I have told you I have seen that your Lord and your Redeemer should do; for, for this cause have they been shown unto me, that ye might know the gate by which ye should enter. For the gate by which ye should enter is repentance and baptism by water; and then cometh a remission of your sins by fire and by the Holy Ghost.
18 And then are ye in this strait and narrow path which leads to eternal life; yea, ye have entered in by the gate; ye have done according to the commandments of the Father and the Son; and ye have received the Holy Ghost, which witnesses of the Father and the Son, unto the fulfilling of the promise which he hath made, that if ye entered in by the way ye should receive.
19 And now, my beloved brethren, after ye have gotten into this strait and narrow path, I would ask if all is done? Behold, I say unto you, Nay; for ye have not come thus far save it were by the word of Christ with unshaken faith in him, relying wholly upon the merits of him who is mighty to save.
20 Wherefore, ye must press forward with a steadfastness in Christ, having a perfect brightness of hope, and a love of God and of all men. Wherefore, if ye shall press forward, feasting upon the word of Christ, and endure to the end, behold, thus saith the Father: Ye shall have eternal life.
21 And now, behold, my beloved brethren, this is the way; and there is none other way nor name given under heaven whereby man can be saved in the kingdom of God. And now, behold, this is the doctrine of Christ, and the only and true doctrine of the Father, and of the Son, and of the Holy Ghost, which is one God, without end. Amen.
The third element, the baptism by fire, deserves a closer examination.
The sole recorded instance of the Lamanites being baptized by fire and the Holy Ghost is in Helaman 5. To be brief, I will cite the pertinent sections, rather than the whole chapter, which is deserving of close study.3 Nephi 9:20
20 And ye shall offer for a sacrifice unto me a broken heart and a contrite spirit. And whoso cometh unto me with a broken heart and a contrite spirit, him will I baptize with fire and with the Holy Ghost, even as the Lamanites, because of their faith in me at the time of their conversion, were baptized with fire and with the Holy Ghost, and they knew it not.
That this is the group the Savior was referring to is affirmed by Moroni.Helaman 5:40-47
40 And it came to pass that the Lamanites said unto him: What shall we do, that this cloud of darkness may be removed from overshadowing us?
41 And Aminadab said unto them: You must repent, and cry unto the voice, even until ye shall have faith in Christ, who was taught unto you by Alma, and Amulek, and Zeezrom; and when ye shall do this, the cloud of darkness shall be removed from overshadowing you.
42 And it came to pass that they all did begin to cry unto the voice of him who had shaken the earth; yea, they did cry even until the cloud of darkness was dispersed.
43 And it came to pass that when they cast their eyes about, and saw that the cloud of darkness was dispersed from overshadowing them, behold, they saw that they were encircled about, yea every soul, by a pillar of fire.
44 And Nephi and Lehi were in the midst of them; yea, they were encircled about; yea, they were as if in the midst of a flaming fire, yet it did harm them not, neither did it take hold upon the walls of the prison; and they were filled with that joy which is unspeakable and full of glory.
45 And behold, the Holy Spirit of God did come down from heaven, and did enter into their hearts, and they were filled as if with fire, and they could speak forth marvelous words.
46 And it came to pass that there came a voice unto them, yea, a pleasant voice, as if it were a whisper, saying:
47 Peace, peace be unto you, because of your faith in my Well Beloved, who was from the foundation of the world.
As used in this verse, "the change" is shorthand for "the mighty change of heart". The baptism by fire is wherein we are, as the scriptures use the phrase, "born again", or "born of the Spirit".Ether 12:14
14 Behold, it was the faith of Nephi and Lehi that wrought the change upon the Lamanites, that they were baptized with fire and with the Holy Ghost.
It is important to note that Adam's actions and experience are here setting the universal pattern - "thus may all become my sons." That is, in this manner anyone has power to become a son of God. From the Lamanites, whom the Savior used as an example of what we should expect, we learn that the baptism by fire and the Holy Ghost comes about by repentance of all one's sins and calling upon the name of the Lord until one has faith in Christ, at which point one receives the baptism by fire and the Holy Ghost, which Nephi informed us is what it means to receive the Holy Ghost (2 Nephi 31:18, cited above); Adam, having beforehand repented, likewise cried unto the Lord to receive this.Moses 6:64-68
64 And it came to pass, when the Lord had spoken with Adam, our father, that Adam cried unto the Lord, and he was caught away by the Spirit of the Lord, and was carried down into the water, and was laid under the water, and was brought forth out of the water.
65 And thus he was baptized, and the Spirit of God descended upon him, and thus he was born of the Spirit, and became quickened in the inner man.
66 And he heard a voice out of heaven, saying: Thou art baptized with fire, and with the Holy Ghost. This is the record of the Father, and the Son, from henceforth and forever;
67 And thou art after the order of him who was without beginning of days or end of years, from all eternity to all eternity.
68 Behold, thou art one in me, a son of God; and thus may all become my sons. Amen.
The signs of this baptism, administered by the Savior himself, following the descriptions of the experiences of Adam and the Lamanites, are minimally as follows.
1. They are born again, or quickened (made alive) in the inner man.
2. They are filled as if by fire by the Holy Ghost.
3. They are filled by a specific joy which is indescribable and full of glory.
4. They are able to speak forth marvellous words - or, in other words, to prophesy, and reveal the things of heaven.
5. They hear the voice of God from on high testifying to them.
All of these things happen quickly; it is a point experience, just as baptism by water is a point experience, just as physical birth is a point experience. This experience is perceptible, pentecostal, eternally life-changing, and bestowed once the preconditions - repentance from all sin (in one's heart, turning away from sin and turning towards God) and exercising faith, by calling upon the name of the Lord until one is received - are met, as affirmed throughout the scripture. Moreover, undergoing this experience is conversion, according to the Savior in 3 Nephi 9:20 (see also 3 Nephi 7:21). That is the scriptural meaning of the word. Since the Savior promises to baptize us by fire and the Holy Ghost, just like the Lamanites, if we come unto him with broken hearts and contrite spirits, everyone may therefore expect if they will repent and cry unto Him until they have faith in Christ that they, too, will immediately receive the same experience.
Even Jesus Himself followed this pattern.
This gift - being converted, being converted unto the Lord, being born again, born of the Spirit, becoming new creatures, taking upon us the name of Christ, receiving the Holy Ghost, receiving the Comforter, being baptized by fire and the Holy Ghost, receiving the mighty change of heart, receiving the image of Christ in one's countenance, becoming a saint through the Atonement of Christ, being sanctified, being made holy and without spot (for all of these are the same thing) - is given if one will lay aside all sin, every worldly lust, all worldly ambition, and call upon God in the name of the Son, asking, with perfect sincerity and faith in Christ, for the remission of one's sins, believing one will receive; as soon as we do this, it is given (see Alma 22:15-18, and Alma 34:31). That is the model of repentance and conversion the Book of Mormon, the Pearl of Great Price, and the Doctrine and Covenants; this is how we make the gospel of Christ effective in our lives.Luke 3:21-22
21 Now when all the people were baptized, it came to pass, that Jesus also being baptized, and praying, the heaven was opened,
22 And the Holy Ghost descended in a bodily shape like a dove upon him, and a voice came from heaven, which said, Thou art my beloved Son; in thee I am well pleased.
This is a minimal sample of the teachings and examples found throughout the scriptures on this particular topic. This may well sum it up.
That is, of course, an instruction to be obeyed literally.2 Nephi 25:29
29 And now behold, I say unto you that the right way is to believe in Christ, and deny him not; and Christ is the Holy One of Israel; wherefore ye must bow down before him, and worship him with all your might, mind, and strength, and your whole soul; and if ye do this ye shall in nowise be cast out.
The reason conversion matters is because the baptism by fire and the Holy Ghost, wherein we are converted, as the word is used scripturally, is guaranteed if we will do the things Christ has taught: repentance (casting aside all sin, turning one's heart fully to God, and calling upon the name of the Lord until one receives a remission of their sins) and baptism, having perfect faith in Him. It is necessary to receive this in order to attain exaltation (D&C 76:52). If we have not received this, it is because we have not repented (turned) from all our sins and called upon the name of the Lord in faith for redemption from them.
The reason focusing upon this teaching cannot be properly considered "gospel hobbyism" or "missing the mark" is because of the commandments of the Lord.Doctrine and Covenants 82:10
10 I, the Lord, am bound when ye do what I say; but when ye do not what I say, ye have no promise.
When speaking to members of record in the Church, one may assume they have been baptized by water; therefore, if a person has not been baptized by fire and the Holy Ghost, and consequentially is not converted, the sole precepts which are to be taught are repentance and faith, which in the Book of Mormon translates to repenting of all sin and calling upon the name of the Lord until one has faith and is received, being given the signs spoken of. That is the plan of redemption. That is the milk of the gospel.Doctrine and Covenants 19:31
31 And of tenets thou shalt not talk, but thou shalt declare repentance and faith on the Savior, and remission of sins by baptism, and by fire, yea, even the Holy Ghost.
Which is why the Nephites proceeded thusly.
What comes after conversion, the mighty change of heart, the baptism by fire and the Holy Ghost wherein we are sanctified, made holy, and without spot, able to prophesy, and hear the word of God from on high? That is where the Lord teaches line upon line, and precept upon precept, by the power of the Spirit which has been received (2 Nephi 32). Much of it is the Law of the Gospel, contained in 3 Nephi 12-15. Notice that 3 Nephi 12 begins with the baptism by fire and the Holy Ghost, and proceeds line upon line and precept upon precept until it ends with this: "Be ye therefore perfect." It is through the baptism by fire and the Holy Ghost, given upon repentance, faith, and baptism, that our nature is changed completely such that we have no more desire to do evil, but to do good continually, that we have power to keep that law, and obey those precepts, from our hearts.Mosiah 25:22
22 And thus, notwithstanding there being many churches they were all one church, yea, even the church of God; for there was nothing preached in all the churches except it were repentance and faith in God.
By laying aside all sin, and turning wholly to God, bowing down before God and calling upon Him with our whole soul, asking to receive the remission of our sins, we are awakened by the power of God into a world filled with the visions and blessings of old returning, and angels visiting the earth (The Spirit of God, Hymn #2); this is what it means to receive the gospel (D&C 39:5-6, cited above), and, so long as we are diligent unto prayer and good works, we retain this gift, being led by the Spirit in all things.
Whatever offense I give you is unintentional; some things matter very greatly, because what a man does is predicated upon what he believes. The gospel of Christ is one of those things, as it invites us to specific, immediate action with a promise of immediate and defined results; and if we don't take that specific, immediate action we have no promise.