Teshuva has many components to it, as we would well expect. There is the sincere regret for having done the transgression in the first place; there is the effort to never do it again; and then there is the vidui - confession. From experience, we all probably realize that the easiest one is the confession, true regret is a bit more difficult, while working at making sure that we never do it again is the one that we usually have the greatest difficulty with. Yet, the Rambam (Hilchos Teshuva 1:1) when defining the mitzvah of teshuva defines it as the act of confessing the sin. Indeed, on Yom Kippur what is clearly repeated again and again is the vidui. To us this seems counterintuitive. We could even imagine a scenario where a person truly regrets his sins, stops doing what he shouldn't do, but never got around to reciting the vidui - confession. We would ask ourselves, "who is the better of the two: the one who confessed but hasn't really succeeded in changing his ways much, or the one who actually changed, but hadn't recited a formal confession?"
To understand this conundrum, we need to go back to the very origins of sin. When the serpent seduced Adam and Chava into sinning, the enticement was not the taste of the fruit. What the serpent told them was, "if you eat from the fruits of this tree, you will be like G-d and understand evil and good." What this means is that Hashem had endowed mankind with extraordinary wisdom. A wisdom that can think far and wide, understand incredible things about the universe he lives in, and create extraordinarily works of depth and understanding. The one thing that the human mind cannot understand in its fullest is the definition of what is truly good and what is truly evil. Great minds have grappled with this issue, which is at the heart of much of philosophical search and thought. Many points have been bandied about, but no two people have ever agreed on the same set of rules. We even struggle to define what actually makes something good and what makes something evil, for good and evil are moral values laid down by Hashem. We can compare, contrast, and expand, but we can never reach the point of being able to independently define good and evil. Being that man was created to be independent, and in a certain sense all-encompassing, this lack of ability frustrates him to his core. It is the one place where man must bow his proud head and say, "You, Almighty One, are the One who knows it and deems it good or bad, and I am simply a servant who needs to follow your direction faultlessly". This admission in a certain sense is a core irritant of the human being, and that is why he so readily fell into the serpent's enticement of, "you will become like G-d to know good from evil."
When we do teshuva, we must always start at the root of our straying from Hashem. Besides the actual deed we did, besides the particular cravings and desires that we had, at the heart of sinning is a deeper root. It is that we decided that something is just fine to do. In every sin there is the tiny speck of, "I will make the decisions about my life, and about what is right and what is wrong." Therefore, without a confession, it may be that a person may change his actions, but he is not really moving away from sin. Imagine the following: a person has been eating treif, and the doctor tells him that meat is deadly for his heart condition and he must immediately give up all meat if he wishes to be healthy. The person, in his desire to be healthy, might listen flawlessly to the doctor and give up all meat. He has in effect stopped eating treif, but he has not moved away one iota from his sin of eating treif. On the other hand, the person who confesses and owns up that Hashem is the one who dictates right and wrong and that he is merely to follow instructions, has taken the first step in the right direction. He may struggle and not be able to move on, but at least he has taken the first step. This is why the heart of teshuva is the vidui - confession.
This also lends insight to an extraordinarily central part of the avodah on Yom Kippur. Of all the sacrifices that we bring on Yom Kippur, the placing of the two goats next to each other, and then casting the lot as to which one would be brought on the mizbeach and which would be thrown off Azazel, is perhaps the strangest of all of the rituals. It is strange for many reasons: firstly, it seems as if the Azazel offering is an offering to powers other than Hashem, which is strictly forbidden. We won't focus on that point. But the very ceremony of drawing lots seems to be a very strange ritual. After all, all of the sacrifices brought had to be first dedicated orally before being brought as a sacrifice, and yet no mention is made of this step, for it is an unimportant prerequisite for bringing a sacrifice. Rather it is the actual act of bringing a sacrifice which is what the avoda is about. And yet when it comes to the two goats, it seems that the ceremony of choosing which one would go on the mizbeach and which one would be cast off Azazel seems to be the highlight. How do we get a sense of that?
In effect, what is happening is that we are going back to the very beginnings of sin, and acting out something that will return us to the acknowledgement that good and evil are all Hashem's to decide. For the halacha is that we must take two goats that are as similar as possible. This means we have standing before us two animals that are indistinguishable to the human eye in every which shape or form. They're similar in height, weight, in price, and in every which way possible. We have no way of deciding which is the ultimate good and which is the ultimate bad. When we cast a lot it is as if we are saying, "Hashem it's Your call". Your hashgacha decides which lot is cast on which animal, and that will designate what is good and bad. The animal that You designate to be brought on the mizbeach is the embodiment of the ultimate good. The animal that You designate to be cast off to the powers of evil, has been designated by you as the embodiment of evil. In effect we are saying to Hashem, "You are the one that is yodea tov vera, and we are clueless".
Yom Kippur is a day of atonement. It is an atonement of the many, many individual sins that have accumulated over the year. We certainly need to examine our actions, regret those that we should not have done, and put into place the mechanisms and disciplines that are necessary to move us forward. We have thus rectified our actions.
But at the deepest level, the attitude and perspective underlying our ease and ability to sin is the thought that, "I know what is right and what is wrong, and no one will tell me differently." On Yom Kippur we come face to face with that poison that the serpent has injected in us, and we say, "Anna Hashem, yes, it is You who sets the standard of good and bad, and I have fallen short of that standard that is Yours to set." Thus begins the process of atonement for the ultimate sin: the sin of the eitz hada'as.