Why is it necessary for us to suffer on the way to repentance for serious transgressions?

Why is it necessary for us to suffer on the way to repentance for serious transgressions? We often think of the results of repentance as simply cleansing us from sin. But that is an incomplete view of the matter. A person who sins is like a tree that bends easily in the wind. On a windy and rainy day the tree bends so deeply against the ground that the leaves become soiled with mud, like sin. If we only focus on cleaning the leaves, the weakness in the tree that allowed it to bend and soil its leaves may remain. Merely cleaning the leaves does not strengthen the tree. Similarly, a person who is merely sorry to be soiled by sin will sin again in the next high wind. The susceptibility to repetition continues until the tree has been strengthened. 

When a person has gone through the process that results in what the scriptures call a broken heart and a contrite spirit, that person is not only eligible to be cleansed from sin. He is also strengthened, and that strengthening is essential for us to realize the purpose of the cleansing, which is to return to our Heavenly Father. To be admitted to his presence we must be more than clean. We must also be changed from a weak person who once transgressed into a strong person with the spiritual stature that qualifies one to dwell in the presence of God. We must, as the scripture says, become “a saint through the atonement of Christ the Lord” (Mosiah 3:19; also see Hafen, The Broken Heart, p. 149). This is what is meant by the scriptural explanation that a person who has repented of his sins will “confess them and forsake them” (D&C 58:43). Forsaking sins is more than resolving not to repeat them. It involves a fundamental change in the individual. (“Sin and Suffering”, Dallin H. Oaks, Ensign Jul 1992. From a fireside address given at Brigham Young University, 5 August 1990. YouTube 24:52)

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The repenting sinner must suffer for his sins, but this suffering has a different purpose than punishment or payment. Its purpose is change (The Lord’s Way. Dallin H. Oaks. [Salt Lake City: Deseret Book, 1991], 223; emphasis in original).

Elder Bruce C. Hafen has written,

The great Mediator asks for our repentance not because we must ‘repay’ him in exchange for his paying our debt to justice, but because repentance initiates a developmental process that, with the Savior’s help, leads us along the path to a saintly character (The Broken Heart [Salt Lake City: Deseret Book, 1989], 149; emphasis in original; Quoted by Brad Wilcox in "His Grace is Sufficient" BYU Devotional 12 Jul 2011).