D&C 20

In the revelation which has become known as "The Articles and Covenants of the Church" the Savior teaches two important doctrines -

"...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 20:30 - 31)

Justification and sanctification being laws of the gospel. Each law satisfied or fulfilled "through the grace of our Lord and Savior Jesus Christ". From the bible dictionary we learn that "grace" -

"... is divine means of help or strength, given through the bounteous mercy and love of Jesus Christ.

It is through the grace of the Lord Jesus, made possible by his atoning sacrifice, that mankind will be raised in immortality, every person receiving his body from the grave in a condition of everlasting life. It is likewise through the grace of the Lord that individuals, through faith in the atonement of Jesus Christ and repentance of their sins, receive strength and assistance to do good works that they otherwise would not be able to maintain if left to their own means. This grace is an enabling power that allows men and women to lay hold on eternal life and exaltation after they have expended their own best efforts.

Divine grace is needed by every soul in consequence of the fall of Adam and also because of man's weaknesses and shortcomings. However, grace cannot suffice without total effort on the part of the recipient. Hence the explanation, "It is by grace that we are saved, after all we can do" (2 Ne. 25:23). It is truly the grace of Jesus Christ that makes salvation possible..." (Bible Dictionary G Grace:Entry)

Of justification, Lehi taught his son -

"...men are instructed sufficiently that they know good from evil. And the law is given unto men. And by the law no flesh is justified..." (Book of Mormon 2 Nephi 2:5)

Many Jews thought just that, that the law of Moses justified them. The law alone does not justify. Obedience to laws is a condition of the law of justification but it requires grace to complete it. Paul taught -

"(For not the hearers of the law are just before God, but the doers of the law shall be justified." (New Testament Romans 2:13)

Elder Bruce R. McConkie defined the law of justification -

"...as being “all covenants, contracts, bonds, obligations, oaths, vows, performances, connections, associations, or expectations (D. & C. 132:7), in which men must abide to be saved and exalted, [that] must be entered into and performed in righteousness so that the Holy Spirit can justify the candidate for salvation in what has been done. . . . An act that is justified by the Spirit is one that is sealed by the Holy Spirit of Promise, or in other words, ratified and approved by the Holy Ghost. This law of justification is the provision the Lord has placed in the gospel to assure that no unrighteous performance will be binding on earth and in heaven, and that no person will add to his position or glory in the hereafter by gaining an unearned blessing.

As with all other doctrines of salvation, justification is available because of the atoning sacrifice of Christ, but it becomes operative in the life of an individual only on conditions of personal righteousness.” (Mormon Doctrine, p. 408.)

Sanctification is when one become clean, pure, and sinless. This can only happen through the power of the atonement of Jesus Christ - again, his grace. Brigham Young explained the law of sanctification as -

"...overcoming every sin and bringing all into subjection to the law of Christ. God has placed in us a pure spirit; when this reigns predominant, without let or hindrance, and triumphs over the flesh and rules and governs and controls as the Lord controls the heavens and the earth, this I call the blessing of sanctification. . . ." (In Journal of Discourses, 10:173.)

It becomes then clear then how these laws are fulfilled -

"...for we know that it is by grace that we are saved, after all we can do." (Book of Mormon 2 Nephi 25:23)