Repentance provides relief to the heart

One of the primary distinguishing features between unbelievers and believers is that believers frequently perform the religious obligation of repentance; since unbelievers try to regard themselves as free of sin, they feel no need to repent. Believers, on the other hand, are unwilling to commit any sin that will displease Allah. However, man, by nature, may sometimes temporarily follow his earthly desires and commit sin but eventually, one regrets and begs for his/her Lord’s forgiveness.
Allah has created human beings as very helpless entities. One may fall into heedlessness due to a lack of knowledge; he may forget even the subjects he knows best, take incorrect decisions and knowingly or otherwise behave in an imperfect manner. That is because human beings have a ruthless enemy who hopes to lead them into rebellion against Allah and to block the true path by sowing doubts in their hearts. There is one side of their nature that constantly commands them to commit evil. Of course, Allah has shown people the way to resist both their earthy desires and the satan who misleads them and has inspired in honest people the power to easily overcome these matters. One would earn the approval and good pleasure of Allah to the extent that one protects himself against these two negative forces.
In any event, Allah shows a way by which people can make good their mistakes; and that way is repentance.

Allah wants people to learn
from their mistakes
One of the wise aspects of believers’ repentance is that they seek shelter in Allah and strive not to repeat their mistakes immediately by feeling a sharp regret: In other words, they perform a genuine and sincere repentance. To repent is to remain true to their intention and word and follow the true course until the time of their death that most pleases Allah. In the Qur’an, Allah describes the way that someone who sincerely repents should behave, “Allah only accepts the repentance of those who do evil in ignorance and then quickly repent after doing it. Allah turns toward such people....” (Qur’an, 4:17) In another verse Allah reveals; “...those who, when they act indecently or wrong themselves, remember Allah and ask forgiveness for their bad actions (and who can forgive bad actions except Allah?) and do not knowingly persist in what they were doing.” (Qur’an, 3:135)
It is very important to repent one’s errors right away and to immediately seek shelter in Allah.
The Holy Qur’an says: “No indeed! Rather what they have earned has rusted up their hearts.” (Qur’an, 83:14)
People must not be deceived by the time allotted to them. During the time they are allowed in the life of this world, they must repent and turn to salvation by seeking forgiveness. That is because faith and repentance at the moment of death may not be valid in the sight of Allah. One must therefore behave as if one might die at any moment and strive to improve one’s moral values.
It must not be forgotten that no matter what mistakes one may make in one’s life, be they great or small, so long as one repents and turns to Allah, the All-Forgiving, He Who accepts all repentance and transforms evil into good, one may hope to be forgiven for one’s past errors. Allah will definitely respond to repentance. He will convert one’s sins into good by forgiving them and will reward one’s present and future good deeds in the best way.
One of the false reasons that people turn away from religious moral values is that people begin to regard themselves as “incorrigible, incapable of improvement” because of the feelings of guilt caused by their misdeeds. Satan constantly works on these people who do not assess matters in terms of the moral values of the Qur’an, and who forget Allah’s titles of the All-Forgiving and All-Merciful, and that He accepts all repentance and is infinitely forgiving, and gives a person who sins the idea that “you are already a sinner, and you cannot change, so accept things as they are.” He will then try to deceive that person by saying, “You have sinned once, so there is no harm in your sinning again,” and thus drag him down.
He uses a person’s errors to turn him away from Allah. However, like all of satan’s tricks, this one is also weak because committing a sin does not mean that the person can never find the true path again. Allah reveals in the Qur’an that He will forgive anyone who sincerely repents, seeks forgiveness and strives not to commit the same sin again: “But if anyone repents after his wrongdoing and puts things right, Allah will turn toward him. Allah is Ever-Forgiving, Most Merciful.” (Qur’an, 5:39)