Musar for Menachot 58:11

The seventh: "He will again have mercy on us" - behold, the Holy One, blessed be He, does not follow the trait of flesh and blood. [That trait is that] if [someone] angers him - if he is appeased from him, he is a little appeased, [but] not like the previous love [he had for him]. But if a person sinned [to God] and he repents, his stature is greater with the Holy One, blessed be He, [than before]. And this is [the meaning of] "In the place that penitents stand, [even] completely righteous ones cannot stand" (Berakhot 34b). And the reason is like they explained in the chapter [entitled] HaBoneh (it is in Menachot 29b in our texts) regarding why [the letter,] hey is made like a portico: "Such that the one that wants to exit from his world [may] exit." The explanation is that the world was created with a hey. And the Holy One, blessed be He, created the world widely open to the side of evil and sin. There is no side that does not have physicality, the evil impulse and defect - like a type of portico. It does not have fences but rather has a large breach, open towards the side of evil, to the bottom side. How many openings are there for anyone who wants to exit from his world - he cannot turn to a side that he will not find a side of sin and iniquity to go out to the external forces (chitsonim)! But it is [also] open from above; so that if he repents, he will be accepted. And they asked, "Let him be taken back through [the bottom]!" [They answered,] "the matter will not help." They [meant] with this that one who repents will not suffice to be fenced from iniquity [with a fence] like the fence of the righteous ones, since they has did not sin - a small fence suffices for them. However a small fence will not suffice for the sinner that sinned and repented. Rather, he needs to fence himself with several difficult fences, since he already breached the small fence once. If he approaches there, his impulse seduces him easily. Rather he needs to distance himself with a very great distancing. And for this [reason], he does not enter through the opening of the portico, where the breach is there. Rather, he ascends and enters through the small opening, [such that] he makes several difficulties and mortifications for himself and [thereby] closes the breaches.

Spelling out what one has done wrong reveals one's inner thoughts, and makes it less likely that such a sin would be committed again. It reveals one's belief that G–d is aware of all his deeds. Having admitted that one had been foolish in sinning and resolving not to do so again, helps to secure G–d's goodwill. G–d, after all, is most interested in the welfare of His creatures. So far the Sefer Hachinuch.