The Promised Messiah^as answers the all-important question, why does man commits sin, and how can he free himself from it. The Promised Messiah^as writes that man is by his very nature averse to things he believes to be harmful, and if he commits sin it is only because he does not truly believe in the existence of God and in the Day of Reckoning. Had he possessed the same certainty about the accountability of sin, as he does, for instance, about the harmfulness of a poison or a snake, he would never even think of transgressing Divine commandments.

Here is a summary from the book of the Promised Messiah^as,  How to be Free from Sin:

“In this article, I intend to show that the remarkable material progress of the current age has been more than counter balanced by its deplorable spiritual decline, to the extent that the souls of men have lost their ability even to grasp obvious truths. It is apparent from a close study of humanity that a hidden and formidable force is pulling it downwards, and man is swiftly being dragged into a pit which is termed Asfalus Safilin [the lowest of the low].

Such a complete change has come over the intellects of men, that they have come to admire and praise things which are abhorrent and detestable to the spiritual eye. Every soul feels itself being dragged downwards by a force, which, through its devastating influence, has already caused a whole world to fall into decline. Pure truths are laughed at and ridiculed, and complete submission to God is looked upon as an absurdity. Every soul is drawn towards the world as if constrained by some hidden force.

As I have often stated before, attraction forms the basis for everything that happens in the world, and the side which possesses greater conviction is able attract others towards itself. There is every truth in the principle that a force can only be counteracted by another more powerful than itself. It is impossible for this world, which is being pulled downwards by the force of base attractions, to rise up again, unless an opposing force appears from heaven to reinforce people’s faith, and to show them that there is more substantial and lasting joy in submission to the commandments of God than in the fulfilment of carnal passions, and to convince them that transgression is worse than death. This heavenly light of conviction is granted to man through the ‘Sun’, i.e., the Imam of his age, and failure to recognize him amounts to dying a death of ignorance. The person who thinks he has no need of this true source of light is deluded, for he sets himself against the immutable laws of God. Human eyes, even though they possess a light of their own, cannot see without the sun. The sun is the source of the light which descends from heaven and illuminates the earth, and without it our eyes are as good as blind. He who attains conviction through this heavenly light is drawn towards piety, and it is natural for a struggle to ensue between the two attractions, one pulling him towards virtue and the other towards vice, one towards the East and the other towards the West. The clash is all the more ferocious when the two attractions are at their peak—as they are during times of tremendous material advancement. As the earth undergoes phenomenal progress, rest assured that spiritual preparations are also being made and an attraction has been formed in heaven to counter the earthly one.
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My answer may invite the response: “Do we not believe in God? Do we not fear Him? Do we not love Him? Do not all people, with the exception of a few, believe in Him? And do they not still commit every kind of sin, and are they not involved in every type of evil and impiety?” I say that there is a great difference between belief and true awareness. I do not say that everyone who believes is able to refrain from sin, I say that only he who truly recognizes God can safeguard himself against it, for he has experienced Divine fear as well as Divine love.

It may also be asked, “Why does Satan disobey God while he possesses true awareness?” The answer is that Satan does not possess the kind of awareness that is bestowed upon those who truly deserve it. Man, by his very nature, is affected by knowledge, and keeps away from the path of destruction when it reveals its hideous countenance. Belief only means accepting something in good faith, but true awareness means to actually experience that belief. It is impossible for true awareness—Ma‘rifat—and sin to dwell in one heart, just as it is impossible for it to be day and night at the same time.

Our everyday experience shows that we are at once drawn towards things that are useful, and shun those we are afraid of. For instance, if you do not know that the thing you are holding in your hand is arsenic, and you imagine that it is only bamboo sugar or some other useful medicine, you will not hesitate to consume ten or even twenty grams of it; but if you know it to be a deadly poison which will kill you instantly, you will never dare to take even a gram of it. Similarly, when man truly realizes that God exists and that every sin is punishable in His eyes, he refrains from every sin, whether it is theft, bloodshed, fornication, cruelty, breach of trust, associating partners with Allah, falsehood, bearing false witness, arrogance, ostentation, acquiring wealth by illegal means, treachery, cursing, fraud, unfaithfulness, leading a life of carelessness, not being grateful to God, not fearing Him, not being compassionate towards His creatures, not remembering Him with fear and humility, being lost in pursuit of worldly comfort and pleasures, forgetting the true Benefactor, being heedless about prayer and humility, selling adulterated goods, not giving in full measure, underselling, not caring for one’s parents, not treating one’s wife with civility, not being obedient to one’s husband, casting evil glances at other men or women, being heedless about the needs of orphans, the weak and helpless, being unmindful of the rights of neighbours, deriding others in order to prove one’s own superiority, mocking at people with words that are meant to hurt them, pointing out someone’s bodily defects in order to humiliate him, calling people by foul names or slandering them, imputing falsehood to God or, God forbid, falsely claiming to be a Prophet or Messenger, denying God’s existence, rebelling against a just ruler, and mischievously creating disorder in the land.

If someone insists that another method for attaining salvation must exist, because belief is not a check against sin, I respond by saying that no one would commit sin if he was sure that lightening would strike him the moment he did so. The logic behind this argument is irrefutable. Just consider, do you ever transgress when you are certain that punishment will be forthcoming? Would you put your hand into a fire, or throw yourself from a mountain, or jump into a well, or lie down before a moving train, or put your hand in the mouth of a wild beast, or happily be bitten by a mad dog, or remain standing in the midst of terrible thunderstorm? Would you not rush out of a house that is about to collapse, or jump out of a bed in which there is a snake, or escape from a building that is on fire? If you are keen to avoid these possible dangers, then why do you not shun those sins that I have just mentioned?

The answer, which a wise person will give after proper deliberation, will be that this contradiction is due to the difference in the way we perceive the two things. Most people do not have sufficient awareness about sin and, even though they consider them to be harmful, do not avoid them as they would avoid a lion or a snake. Deep in their hearts, they do not really believe that they will be punished for their sins. They even doubt whether God really exists, and, if He does, whether their souls will survive after death, and, if they do, whether or not they will actually be punished for their sins. Most people do harbour such thoughts without being aware of them. But, at the same time, they avoid all the dangers that I have mentioned above, because they fear certain death if they go near them, and if they come face to face with such a danger they waste no time running away from it. The fact is that man is certain about the harmful effects of these things, but in the case of religious injunctions, he is not so sure and his knowledge is based only on conjecture and myth, instead of personal experience, and myths cannot help a man to free himself from sin.
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English Book: How to be Free from Sin
Urdu Book: How to be Free from Sin