What is the Law of justification? It is simply this "All covenants, contracts, bonds, obligations, oaths, vows, performances, connections, associations, or expectations (D&C132:7), in which men must abide to be saved and exalted, must be entered into and performed in righteousness so that the Holy Spirit can justify the candidate for salvation in what has been done. (1 Ne. 16:2; Jac. 2:13-14; Alma 41:15, D&C 98; 132:1, 62.) 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. The 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.
Mormon Doctrine p. 408
I don't think I said anything different on the subject that McConkie didn't say also. Sanctification is tied into this principle.
Moro. 10:32-33
32 Yea, come unto Christ, and be perfected in him, and deny yourselves of all ungodliness; and if ye shall deny yourselves of all ungodliness, and love God with all your might, mind and strength, then is his grace sufficient for you, that by his grace ye may be perfect in Christ; and if by the grace of God ye are perfect in Christ, ye can in nowise deny the power of God.
33 And again, if ye by the grace of God are perfect in Christ, and deny not his power, then are ye sanctified in Christ by the grace of God, through the shedding of the blood of Christ, which is in the covenant of the Father unto the remission of your sins, that ye become holy, without spot.
The commandment is to sanctify ourselves. (D&C 39:18) This is accomplished by being obedient to the "law of Christ" (D&C 88:21, 34-35)and is posible because of his atoning sacrifice. (D&C 76:41) And "all those who will not endure chastening, but deny me," saith the Lord, "Cannot be sanctified." (D&C 101:5)
We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light. - Plato