Parshas Vayikra enumerates many korbanos, including those that must be given for inadvertent sins. Why must a person give a korban for a sin that he did not flagrantly intend to commit? The commentaries explain that the fact that he allowed himself to commit such a sin, even inadvertently, demonstrates an element of carelessness. Had he been more zahir, he would never have allowed himself to get to the point where he could sin. The Torah goes even further and requires that a person who has a doubt as to whether he committed a sin that requires a korban, is required to bring an asham talui. The Sefer HaChinuch explains that this korban does not atone for the actual sin (if it was indeed committed), rather it serves as an atonement for the carelessness that caused the safek.
It still needs to be understood what is the root cause of the carelessness that leads to inadvertent sins and why bringing korbanos helped atone for it. In order to answer this, it is instructive to compare how we conduct ourselves in the physical world with how we act with regard to spiritual matters. If a person is aware that a poisonous substance may be present in the food that he intends to eat he would be extremely careful to avoid any remote possibility of consuming the poison. This is because he is well aware of the dire consequences of eating poison. Just as there are natural consequences to our actions in the physical world, there are also natural consequences to actions in the spiritual world. Therefore, a person who is faced with the possibility of eating food that is forbidden, such as chelev, should have the same level of zehirus to avoid doing something that will cause him grave spiritual damage. When a person stumbles and sins inadvertently or puts himself in a position where he is in doubt as to whether he sinned, he demonstrates a lack of sensitivity to the spiritual consequences of his actions; he is not fully cognizant of the spiritual reality that negative actions inevitably have negative results.
There seem to be two main reasons as to why it is far more difficult to attain the same awareness of cause-and-effect in the spiritual world as in the physical world: Firstly, the physical world is completely tangible to us - we can easily see the results of our actions, for example, when a person eats poison, he is visibly damaged. In contrast, the spiritual world is not tangible and we cannot see the results of our actions - for example, a person is less aware of the spiritual consequences of breaking Shabbos b’shogeg, because he has never visually seen them. If he could see what happens in the spiritual realm for turning a light on, forgetting that it is Shabbos, then he would surely never allow himself to commit that sin b’shogeg.
Giving a korban for committing such an aveiro helped a person metaken this flaw of not being real with spiritual consequences. He had to go through a lengthy and expensive process of paying for, and bringing a korban to Yerushalayim, and go through the dramatic process of offering up the korban and seeing its blood. This process surely made it very clear that there are dramatic consequences to one’s actions.
The second reason why it is difficult to live with the awareness that there are consequences to all our actions in the spiritual world, is that we are so familiar with Hashem’s ‘mida‘ of Rachamim that it is easy slip into the trap of thinking that Hashem will automatically forgive us for our sins. As a result, a person will be less fearful of the consequences of sinning. The Gemara in Chagiga observes that there is a natural yetser hara to presume that there is automatic forgiveness for sinning - it states, “If the yetser hara will tell you, ‘sin and Hashem will forgive you,’ do not listen to him.”
The Mesillas Yesharim addresses this attitude at length and stresses that it is incorrect - Hashem is a ‘Kel Emes’ who judges every action. Hashem’s rachamim does not contradict the concept of reward and punishment: Rachamim does three things; it delays the punishment from taking place immediately giving a person a chance to do teshuva; it causes the onesh to be handed out in smaller, more manageable doses; and it gives us the opportunity to do teshuva and thereby gain complete forgiveness. There is, nonetheless, judgement for every outcome and an awareness of this should cause a person to be far more zahir from sinning. Offering a korban also helped rectify the attitude that Hashem is a vatran. By going through the arduous process of offering the korban, the person would see that he could not gain forgiveness without teshuva.
We do not have the opportunity to offer korbanos for our inadvertent sins, and as a result we do not have this essential tool to help make us aware of the reality of chet. How can we engrain this into ourselves? There are many accounts of Gedolim who saw the spiritual world as tangibly as the physical world: On one occasion, Rav Moshe Feinstein zt”l was asked to leave the Beis Medrash in order to take an important phone call from another country, but he could not get to the phone because somebody was davenning the Shemoneh Esrei in front of the door and his ‘dalet amos’ was blocking the exit. When asked why he would not leave for such an important and costly call, he said that there was a wall blocking him and he could not walk through a wall. For Rav Moshe, ‘dalet amos’ was not some vague concept, it was a clear reality. His Gadlus in Torah was surely the cause of such a tangible sense of Yiras Shamayim - it was not just that he knew all of Torah, but that he allowed it to become so much a part of him that it became so real in his mind. A person can learn Torah in an intellectual way and not let it filter into his being - that kind of learning will probably not be so effective in increasing one’s yiras Shamayim - learning with an appreciation that it is discussing reality and trying to apply it to our lives will hopefully enable a person to be more real with the spiritual world.
A second aitsa is that of Rav Yisroel Salanter - that if a person wants to develop more of a sensitivity in a certain area of halacho, he should learn that area in depth - this will naturally bring him to a much greater awareness of his actions in that area. For example, whenever Rav Yisroel would find himself in a situation that could lead to yichud, he would learn the sugyas of yichud in great depth, in this way assuring himself that he would maintain constant awareness of any possibility of yichud. One particular area where this principle is very important is that of lashon hara: There is such a constant nisayon to speak lashon hara that without learning the laws of lashon hara it is extremely difficult to avoid the numerous pitfalls that arise. By learning the laws, as well as knowing what constitutes forbidden speech, a person will develop a far greater sensitivity in his speech.
There is one final exercise that can help increase our level of zehirus: Imagine if someone offered a Torah observant person $100 to speak lashon hara - the person would immediately refuse. What if he offered $1000, or $10,000 or $1000,000?! A person with a clear Torah hashakfa will refuse any amount of money rather than commit a sin because he is intellectually aware that the onesh for speaking lashon hara will be infinitely greater than anything finite. And yet, a person may often speak lashon hara for no money at all! The difference between the two situations is that when a person is clear that what he will do is an aveiro he has intellectual clarity that this is very bad for his neshama. However, without such clarity, b’shaas maaseh, a person rationalizes that what he is about to say is not really lashon hara and allows himself to say it regardless of the possible consequences of such a severe sin. We see from here that a person has the strength to withstand sin when he has total clarity that what he is about to do constitutes an issur. Developing a sense of clarity and intellectual honesty as to when we are committing an aveiro will enable us to tap into this koyach and give us the strength to withstand sin.
We do not have the gift of korbanos anymore, but the lessons that we learn from them can help us develop a strong sense of yiras shamayim that can prevent us from the damage
 Vayikra, 5:17.
 Sefer Hachinuch, Mitzvo 128. Also see Seforno, Vayikra, 15:17.
 Chagiga, 16a.
 Mesillas Yesharim, Ch.4, p.41-2..