It is very important for our spiritual and emotional life to pay special attention to repentance, the greatest shelter against sins, in the following respects:
Reaction to Sin
One's reaction to a sin that he or she has committed is closely related to one's moral and spiritual station. There may be an instance in which, because of a sin, you prostrate yourself before God and implore Him to forgive you. There may also be a case when such actions do not satisfy you, when your sorrow lights an internal fire in your heart. But we can hope that the sorrow disturbing your heart in the name of repentance may be more acceptable to God.
Repentance is indeed regret and an internal fever. In this respect, one should regard sins as being in the company of serpents and poisonous centipedes. Only such a firm attitude is acceptable from a believer, for any contrary one implies doubts about the outcomes of a sin in the Hereafter. Therefore, it is essential that every sin be confronted in an alert manner and, if committed, be succeeded by regret.
Sins Must Be Short-Lived
Since every sin engenders a new sin, whenever a person commits a sin, he or she must seek purification without delay. After all, no one knows when he or she will pass away. Those who are conscious of God cannot be at ease until they have cleansed themselves from sin. It is detrimental to a person's spiritual well-being if he or she allows a sin to survive for even one second. Moreover, such an attitude implies revering something that God does not like. Sins do not have the right to live. They must be ephemeral, because if they are not removed through repentance they become serpents constantly biting one's heart. And once the heart gets a stain, it is easier to get more. The end result is a vicious circle. Every sin engenders a new sin and at last, Indeed, on their hearts is the stain of the (ill) that they do (Mutaffifin 83:14) becomes evident on them.
For this reason, it is very important to remind people of these realities and alert them to sins. Moreover, if you can do so, you must reveal the ugly nature of sin to people and make them renounce their sins.
Apparently, sensitive and alert souls can smell the offensive odor that sins exude.
Sins Must Be Regarded as Detestable
When repenting, one of the most important things is to view the particular sin as something detestable and disgusting. If we do not abstain from sins, believing that they are like being with serpents and scorpions and therefore deserve our disgust, we will not have the resolve to struggle against them through repentance. When you break a priceless crystal vase, for example, you feel sorrow. In the same way, every sin you commit cracks and dirties your life lantern. Thus it is necessary to feel regret and sorrow after each sin, at least to the degree of sorrow felt after breaking a crystal vase. Otherwise, you are not taking your sins and your repentance seriously.
The Correspondence between Sin and Repentance
One's repentance for a given sin must match the sin's degree of seriousness, for every sin resembles a well filled with pitch. In other words, it is easy to fall into but very hard to get out of.
If we belittle the outcomes of a sin, we are committing another sin equivalent to the first one. For instance, if one considers fornication or violation of another's property rights as sins exaggerated by religion and says that "we benefit from them, so why consider them sins?" he or she is committing an even bigger sin. Thus, we have to resist sins and condition ourselves in this way: "O sins, the doors of my heart are locked, so your zeal to get into my heart is in vain."
The simile of the great scholar Bediüzzaman Said Nursi is very expressive: "Run away from a sin as if it is a poisonous serpent or a centipede." Note that he likens sin to a serpent and a centipede, rather than a lion or a tiger. One can take measures before a lion or a tiger attacks, for they attack bravely, whereas a serpent and a centipede attacks unexpectedly and maliciously. Backstabbing and treachery may be considered examples of such sins.
In short, vigilance against sins must be an attribute of a true believer. We have to keep in mind that vigilance against sins is an indication of our loyalty and fidelity to our Lord, the Almighty.
To realize the true nature of sins, we can look from the point of view of holy saying of Prophet Muhammad: "Adhnaba 'abdi dhanban," which is about a servant of God who sins and then repents. In this saying, the words used have a very deep meaning: dhanb (sin) and dhanab (tail) come from the same root in Arabic. Thus, a believer who says: "O my Lord, I have committed a sin," means to say: "O my Lord, I have put on a tail again. In my present state, You may consider me a fox with a furry tail, a scorpion stinging others with its tail, or a serpent whose tail is a long part of its body! And that is me!" In other words, those who confess their sins in reality confess that they have scorned and belittled the humanity granted to them by God and, as a result, have fallen to the level of the animals.
As for the one who sins and is unaware of it, he or she is a mirror of the verse: They are like cattle, or rather are even more misguided (7:179) and has fallen to a level below the animals.
 Muslim, Tawba, 29-30