It isn’t necessary to believe in God to desire forgiveness for our transgressions towards other people. Guilt and other negative consequences of sin spur us to seek after peace and contentment. Experiencing negative emotions or consequences is quite common, though it does not typically yield lasting change, and it is certainly insufficient to entice a person to undergo the harrowing transformation that is required for a person to experience joy in the presence of God.
An understanding of the love of God cannot be obtained or increased in a way that yields joy except through faith. God could reveal his love to anyone, at any time, to any degree, but doing so outside of the faith process would fill the recipient with indescribable agony due to the inescapable guilt with which it would fill them. Faith is the only mechanism through which a person can gain an understanding of the love of God in a way that yields joy because the need to choose and act on the part of the participant releases them from the guilt they would otherwise feel. One who has faith in Christ will not only gain a greater understanding of the love of God, but they will also reform their beliefs and actions to conform to their understanding of God as it improves in accuracy and depth.
Whenever a person is truly converted to God, it is through an increased understanding of his love. There are many examples of this in scripture.
When Alma began to understand the love of God, he was so racked with his guilt that he laid on the ground in paralyzed silence for three days. He said:
12 But I was racked with eternal torment, for my soul was harrowed up to the greatest degree and racked with all my sins.
13 Yea, I did remember all my sins and iniquities, for which I was tormented with the pains of hell; yea, I saw that I had rebelled against my God, and that I had not kept his holy commandments.
14 Yea, and I had murdered many of his children, or rather led them away unto destruction; yea, and in fine so great had been my iniquities, that the very thought of coming into the presence of my God did rack my soul with inexpressible horror.
15 Oh, thought I, that I could be banished and become extinct both soul and body, that I might not be brought to stand in the presence of my God, to be judged of my deeds.
16 And now, for three days and for three nights was I racked, even with the pains of a damned soul.
17 And it came to pass that as I was thus racked with torment, while I was harrowed up by the memory of my many sins, behold, I remembered also to have heard my father prophesy unto the people concerning the coming of one Jesus Christ, a Son of God, to atone for the sins of the world.
18 Now, as my mind caught hold upon this thought, I cried within my heart: O Jesus, thou Son of God, have mercy on me, who am in the gall of bitterness, and am encircled about by the everlasting chains of death. (Alma 36)
When the Lord appeared to Paul and told him that his zealous persecution of the Christians was wrong, his turmoil was so great that he went without food and water for three days (see Acts 9:4-9).
When Zeezrom heard the gospel preached by Alma and Amulek, “his soul began to be harrowed up under a consciousness of his own guilt; yea, he began to be encircled about by the pains of hell.” (Alma 14:6)
The guilt experienced by those who, through faith, have gained an understanding of the love of God is a measured dose of what we will feel at judgment if we are not reconciled to God. If we take that dose and use it to come to a full understanding of the reality and contents of judgment day, we will believe that hell is worse than any pleasure offered by sin:
Prepare your souls for that glorious day when justice shall be administered unto the righteous, even the day of judgment, that ye may not shrink with awful fear; that ye may not remember your awful guilt in perfectness, and be constrained to exclaim: Holy, holy are thy judgments, O Lord God Almighty—but I know my guilt; I transgressed thy law, and my transgressions are mine; and the devil hath obtained me, that I am a prey to his awful misery. (2 Nephi 9:46)
Jesus pointed out that those who are forgiven of much will be much more grateful than those who are forgiven of little:
36 And one of the Pharisees desired him that he would eat with him. And he went into the Pharisee’s house, and sat down to meat.
37 And, behold, a woman in the city, which was a sinner, when she knew that Jesus sat at meat in the Pharisee’s house, brought an alabaster box of ointment,
38 And stood at his feet behind him weeping, and began to wash his feet with tears, and did wipe them with the hairs of her head, and kissed his feet, and anointed them with the ointment.
39 Now when the Pharisee which had bidden him saw it, he spake within himself, saying, This man, if he were a prophet, would have known who and what manner of woman this is that toucheth him: for she is a sinner.
40 And Jesus answering said unto him, Simon, I have somewhat to say unto thee. And he saith, Master, say on.
41 There was a certain creditor which had two debtors: the one owed five hundred pence, and the other fifty.
42 And when they had nothing to pay, he frankly forgave them both. Tell me therefore, which of them will love him most?
43 Simon answered and said, I suppose that he, to whom he forgave most. And he said unto him, Thou hast rightly judged.
44 And he turned to the woman, and said unto Simon, Seest thou this woman? I entered into thine house, thou gavest me no water for my feet: but she hath washed my feet with tears, and wiped them with the hairs of her head.
45 Thou gavest me no kiss: but this woman since the time I came in hath not ceased to kiss my feet.
46 My head with oil thou didst not anoint: but this woman hath anointed my feet with ointment.
47 Wherefore I say unto thee, Her sins, which are many, are forgiven; for she loved much: but to whom little is forgiven, the same loveth little. (Luke 7)
One interesting aspect of this account is that both debtors would have been under the same consequence of prison or enslavement for their debts. While our gratitude indeed differs, it only does so commensurate with our perception of the degree of offense we have committed. In reality, all sin is equally sufficient to cause eternal torment: a sinner in one is a sinner in all: “For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.” (James 2:10)
Desire for Christ must be consummate in order to bring about forgiveness. For many outcomes, a light desire is insufficient, and when it comes to a desire for forgiveness of past sins, nothing less than everything will do. Anything less than an absolute, sincere surrender to God will not free you from the guilt of your past sins. You “must bow down before him, and worship him with all your might, mind, and strength, and your whole soul.” (2 Nephi 25:29)
The scriptures provide examples of what this looks like in practice. When a proud king was taught the gospel,
17 ...the king did bow down before the Lord, upon his knees; yea, even he did prostrate himself upon the earth, and cried mightily, saying:
18 O God, Aaron hath told me that there is a God; and if there is a God, and if thou art God, wilt thou make thyself known unto me, and I will give away all my sins to know thee, and that I may be raised from the dead, and be saved at the last day.... (Alma 22)
Forgiveness of past sins not only frees a person from the guilt of knowing that they could have done better, but also provides motivation for abstaining from future sin. One cannot be forgiven by God without recognizing a greater portion of God’s love, which in turn makes them love him more (see Luke 7:47).
Without forgiveness of past sin, future sinlessness could not bring the peace and contentment it qualifies for, as the guilt and sorrow for past sins would endure no matter how perfect one’s future actions might be:
15 Do ye exercise faith in the redemption of him who created you? Do you look forward with an eye of faith, and view this mortal body raised in immortality, and this corruption raised in incorruption, to stand before God to be judged according to the deeds which have been done in the mortal body?
16 I say unto you, can you imagine to yourselves that ye hear the voice of the Lord, saying unto you, in that day: Come unto me ye blessed, for behold, your works have been the works of righteousness upon the face of the earth?
17 Or do ye imagine to yourselves that ye can lie unto the Lord in that day, and say—Lord, our works have been righteous works upon the face of the earth—and that he will save you?
18 Or otherwise, can ye imagine yourselves brought before the tribunal of God with your souls filled with guilt and remorse, having a remembrance of all your guilt, yea, a perfect remembrance of all your wickedness, yea, a remembrance that ye have set at defiance the commandments of God?
19 I say unto you, can ye look up to God at that day with a pure heart and clean hands? I say unto you, can you look up, having the image of God engraven upon your countenances?
20 I say unto you, can ye think of being saved when you have yielded yourselves to become subjects to the devil?
21 I say unto you, ye will know at that day that ye cannot be saved; for there can no man be saved except his garments are washed white; yea, his garments must be purified until they are cleansed from all stain, through the blood of him of whom it has been spoken by our fathers, who should come to redeem his people from their sins.
22 And now I ask of you, my brethren, how will any of you feel, if ye shall stand before the bar of God, having your garments stained with blood and all manner of filthiness? Behold, what will these things testify against you? (Alma 5)
Because perceived value leads to desire, one’s degree of understanding of the value of forgiveness through Christ will determine one’s desire to obtain it. One who desires to change because of the love of God will do more for longer than one who does not. One who understands the love of God will value aligning their actions with his more than anything in this world.