D&C 20

Much like the current Handbook of Instructions, this revelation of instructions for the newly restored Church first includes an brief summary of the plan of salvation for as Alma taught that -

"Therefore God gave unto them commandments, after having made known unto them the plan of redemption..."  (Book of Mormon | Alma 12:32)

In this revelation, again the Lord makes known the plan of redemption, first declaring -

"...we know that there is a God in heaven, who is infinite and eternal, from everlasting to everlasting the same unchangeable God, the framer of heaven and earth, and all things which are in them;
18  And that he created man, male and female, after his own image and in his own likeness, created he them..."  (Doctrine and Covenants | Section 20:17 - 18)

Then He -

"...gave unto them commandments that they should love and serve him, the only living and true God, and that he should be the only being whom they should worship."  (Doctrine and Covenants | Section 20:19)

"But by the transgression of these holy laws man became sensual and devilish, and became fallen man."  (Doctrine and Covenants | Section 20:20)

From the beginning we have been given our agency.  Then we were given knowledge or commandments.  It is how we use our agency that determines if we become fallen or sensual and devilish.  It is important to understand that we are not born that way for we know the children are innocent.  It is as we reach an age of accountability with an understanding of the knowledge given us that we cause ourselves to become fallen.  There is no mortal man, because of agency, that has not made mistakes (except the Savior). And thus -

"...the Almighty God gave his Only Begotten Son, as it is written in those scriptures which have been given of him.
22  He suffered temptations but gave no heed unto them.
23  He was crucified, died, and rose again the third day;
24  And ascended into heaven, to sit down on the right hand of the Father, to reign with almighty power according to the will of the Father..."  (Doctrine and Covenants | Section 20:21 - 24)

Having thus provided the infinite atonement, God set conditions to receive the blessings of the atonement over spiritual death or fallen man due to not keeping the commandments being -

"That as many as would believe and be baptized in his holy name, and endure in faith to the end, should be saved—
26  Not only those who believed after he came in the meridian of time, in the flesh, but all those from the beginning, even as many as were before he came, who believed in the words of the holy prophets, who spake as they were inspired by the gift of the Holy Ghost, who truly testified of him in all things, should have eternal life,
27  As well as those who should come after, who should believe in the gifts and callings of God by the Holy Ghost, which beareth record of the Father and of the Son..."  (Doctrine and Covenants | Section 20:25 - 27)

"And we know that all men must repent and believe on the name of Jesus Christ, and worship the Father in his name, and endure in faith on his name to the end, or they cannot be saved in the kingdom of God.
30  And we know that justification through the grace of our Lord and Savior Jesus Christ is just and true;
31  And we know also, that sanctification through the grace of our Lord and Savior Jesus Christ is just and true, to all those who love and serve God with all their mights, minds, and strength."  (Doctrine and Covenants | Section 20:29 - 31)

This is the doctrine of Christ and the basic plan of redemption for  -

"...we know that these things are true and according to the revelations of John, neither adding to, nor diminishing from the prophecy of his book, the holy scriptures, or the revelations of God which shall come hereafter by the gift and power of the Holy Ghost, the voice of God, or the ministering of angels."  (Doctrine and Covenants | Section 20:35)

This is why we follow the instructions for this new organized Church.