To summarize [according to my understanding]:
The pasuk כי יחטאו לך כי אין אדם אשר לא יחטא ואנפת בם implies that we are punished even for sins that are not in the realm of our free choice. Why?
When we sin purposefully, we show that we have no problems even commiting the sins we did accidentally.
Similarly, we never know when our free choice was denied us and we HAD to sin. By not doing teshuva on ALL our sins we are showing that even those sins committed due to a lack of free choice were ultimately in accordance with our will. Otherwise, how could we not do teshuva on all our sins just in case each one was committed by choice....
Hashem "wants teshuva" [הרוצה בתשובה, even though he clearly does not want us to sin in the first place] because of those sins that He DID want us to commit. Namely, those sins done without free choice where we should be doing teshuva because we didn't know if we had free choice or not. Otherwise, we show that we don't care.
This pasuk was said at the end of the building of the Beis Hamikdash. The Beis Hamikdash doesn't have the power to prevent us from sinning completely [because as we said some sins are beyond our control] but does bring us atonement for sins already committed. We mention those sins we committed without free choice so that we are not guilty of "opening our mouths to the Satan" and bringing upon ourselves sins that we would not have otherwise committed [i.e. those with free choice]. Once we mention the power of teshuva of one who davens towards the Beis Hamikdash for sins committed without free choice [for the aforementioned reason], it also can include those sins committed with free choice.
These divrei Torah should be a zchus for R' Simcha Yusopov and his Rebbetzin upon the birth of their ben habechor!!! May he grow up to be a holy, sweet Jew like his parents and live a life of SIMCHA, health and prosperity.