It's about the Doctrine of Christ.
He has given us this life as an opportunity to gain a physical body, to experience trials and temptations, and to overcome them using our free agency. These are all essential parts of the Plan for us to become like our Father in Heaven. At the center of this Plan is the Atonement of Jesus Christ. Our All-knowing Father knew from the beginning that we would make mistakes; mistakes that would separate us from Him physically and spiritually. For the purpose of making available to us, his children, the ability to repent and overcome these mistakes, thus having the opportunity to return to His presence in the flesh, the Greatest of all His spirit children was foreordained to be our Savior and Exemplar, even Jesus Christ.
Through His Atonement we can be cleansed from sin. The Savior satisfied the demands of justice, that unchanging law, so that mercy could be extended to those who believe on His name in the day of judgement. Our faith in Him, faith that He performed the Atonement, that He truly is the Son of God, is essential. It is the first principle of the gospel. We cannot obtain a remission of our sins without it, for a remission of sins can come from no other source than He who suffered to take the penalty of all sins upon Himself.
True faith in the Savior leads to action. Through the Atonement of Jesus Christ, all men are redeemed from the fall. "All little children are alive in Christ" (Moroni 8:22), having known no sin; and all people will be resurrected with an immortal body of flesh and bone. However, for the Savior's Atonement to have effect on us, so far as to cleanse us from the sins we have committed, we must humble ourselves, forsaking our own will for that of the Father. As we do this, we will change our lives to be in harmony with the Savior's teachings and commandments. We will make recompense for the wrongs we have done. We will strive to become more like the Savior, and seek to share His Gospel with others. This is the process of repentance. True repentance comes from our love of the Savior, and an earnest desire to please Him, and to keep and do His teachings.
As our Exemplar, Jesus took part in the ordinance of baptism. Though the Father knows our hearts, baptism by immersion is the way prescribed by Him as an outward expression of our inner desire, and the way by which we can enter into a covenant with Him. Jesus taught the inquiring Pharisee, Nicodemus, "Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God." (John 3:5)
The reception of the Holy Ghost here referenced is a great gift from God. The Spirit sanctifies us, and is given as a Comforter and Guide to all those who have been baptized and strive to live according to the will of the Father.
The prophet Nephi taught: "Wherefore, my beloved brethren, I know that if ye shall follow the Son, with full purpose of heart, acting no hypocrisy and no deception before God, but with real intent, repenting of your sins, witnessing unto the Father that ye are willing to take upon you the name of Christ, by baptism—yea, by following your Lord and your Savior down into the water, according to his word, behold, then shall ye receive the Holy Ghost; yea, then cometh the baptism of fire and of the Holy Ghost; and then can ye speak with the tongue of angels, and shout praises unto the Holy One of Israel." (2 Nephi 31:13)
Our submission to the will of the Father in doing these things will bring peace in this life, and eternal joy in the life to come. This is the Doctrine of Christ. This is His Gospel, the good news that we are called to share. May those we teach understand this amazing message. In the name of Jesus Christ, Amen.