When Jesus Christ was upon the earth, He taught the fulness of His doctrine, which is the plan that our Heavenly Father has outlined for the eternal progress of His children. Later, many of these gospel truths were lost through being diluted by the principles or philosophies then prevailing in the world where Christianity was preached and through the manipulations of political leaders. We call this loss of the fulness of truth the Apostasy.
Many church denominations or philosophies that exist in the world today contain, in greater or lesser measure, truths revealed by God in earlier days, along with a mixture of the philosophies or manipulations of men. We believe that most religious leaders and followers are sincere believers who love God and understand and serve Him to the best of their abilities. We are indebted to the men and women who kept the light of faith and learning alive through the centuries to the present day. We want all who investigate our church from other churches or systems of belief to retain everything they have that is good and to come and see how we can add to their understanding of truth and to their happiness as they follow it.
Because so much had been lost in the Apostasy, it was necessary that the Lord restore the fulness of His doctrine. That began with what we call Joseph Smith's First Vision.
The fulness of the gospel of Jesus Christ begins with the assurance that we lived as spirits before we came to this earth. It affirms that this mortal life has a purpose. It teaches that our highest aspiration is to become like our heavenly parents. We do this by qualifying for the glorified celestial condition and relationships that are called exaltation or eternal life, which will empower us to perpetuate our family relationships throughout eternity.
The doctrine of Jesus Christ, understood in its fulness, is the plan by which we can become what children of God are supposed to become. This spotless and perfected state will result from a steady succession of covenants, ordinances, and actions; an accumulation of right choices; and continuing repentance. "This life is the time for men to prepare to meet God" (Alma 34:32). This is made possible through the Atonement of Jesus Christ and by obedience to the laws and ordinances of His gospel.
The restored gospel of Jesus Christ is comprehensive, universal, merciful, and true. Following the necessary experience of mortal life, all sons and daughters of God will be resurrected and go to a kingdom of glory more wonderful than any mortals can comprehend. With only a few exceptions, even the very wicked will ultimately go to a marvelous—though lesser—kingdom of glory. All of this will occur because of God's great love for His children, and it is all made possible because of the Atonement and Resurrection of Jesus Christ, "who glorifies the Father, and saves all the works of his hands" (D&C 76:43).