In these chapters of the Book of Mormon, the prophet Alma gives counsel to his three sons, Helaman, Corianton, and Shiblon concerning righteousness and the plan of our Savior Jesus Christ for the salvation of mankind.
Satan would have us selfishly serve our own desires and, in a sense, make our whims a god over our lives. His sole purpose is to frustrate the plan of salvation, causing others the same condemnation that he must face. Satan will never have a body and will never enjoy the blessings of being exalted in heaven with Heavenly Father and Jesus Christ, and he wants to do all he can to drag others down with him. Our actions in this earthly state matter because of the Law of Restoration, which states that "that which ye do send out shall return unto you again, and be restored; therefore, the word restoration more fully condemneth the sinner, and justifieth him not at all" (Alma 41:15). Good is restored to good, and evil to evil in the Resurrection. As Alma points out, "wickedness never was happiness" (Alma 41:10). You simply cannot act immorally and wickedly and find true, lasting happiness.
Jesus Christ, on the other hand, has a much different plan for us. There is a Plan of Salvation in which mankind is created, fallen, redeemed through the Crucifixion, and then resurrected and can be exalted to eternity with Heavenly Father and Jesus Christ. Under the gospel of Jesus Christ, people must first obtain faith in the Lord and Savior Jesus Christ. They must repent of their sins and receive a remission of their sins through baptism by immersion. Finally, people must live righteously, following God's commandments and enduring to the end. The gospel of Christ is simple to understand. The difficulty comes in implementing it in our lives and staying faithful to it. Thankfully, we are able to repent of our inevitable mistakes and can strive to be a little better each day. This plan of happiness is the only "way or means whereby man can be saved" (Alma 38:9). In this earthly life, we are given agency and free will to choose how we will conduct our lives. Life is a "time granted unto men to repent...a probationary time...to repent and serve God" (Alma 42:4). Let us all try in our lives to be diligent in following the commandments of the Lord, and be accountable and repentant for our sins.