Why does it say "Ken Amartem?"?
Rashi: You do not want to repent, for you think that Teshuvah will not help you. Malbim ? they have two reasons to say so. (a) They compare Hashem's Mitzvos and warnings to a king who commanded his servants, and they transgressed his command. They are liable for rebellion against the king, and for ruining his work. For both of them, Teshuvah and regret do not help! (b) Mitzvos and warnings are for our benefit, like a doctor commands a patient. They come to purify and sanctify our Nefashos. If the patient transgresses the doctor's words, he will melt in his illness. Teshuvah and regret will not help!
Radak: This is like "Ken Bnos Tzlafchad Dovros" (Bamidbar 27:7; they speak correctly).
Why do they say "Pesha'enu v'Chatoseinu Aleinu"?
Radak: If you thought so you thought well. I.e. if you will confess over your sins it will be good, and you will admit that the evils that come upon you are due to your sins ? they are not chance!
Malbim: Pashanu (we rebelled) against the King of the world, and our Shogeg sins are on us ? the deeds themselves. We ruined His work and Avodah. How can Teshuvah help?!
What is the meaning of "Nimakim"?
Radak: The root is Makak; it is Nif'al conjugation. It is like "Hamek Besaro" (Zecharyah 14:12), "Yimaku 1 ba'Avonam" (Vayikra 26:39).
All explain "Yimaku" to be melting, and so some explain also "Hamek"; Rashi and Radak said that Hamek is limbs falling off. (PF)
QUESTIONS ON RASHI
Rashi writes that they thought that Teshuvah will not help. Why did they think so?
Ohr Yisrael (Kochvei Ohr 3, DH uv'Zos Nimtza): They saw Kevod Hashem dwell in the Mikdash and fathomed His grandeur far more than us, so they appreciated how great is their sin. It opposes intellect to say that Teshuvah can help. We have no difficulty believing that Teshuvah can help, for we cannot fathom His grandeur, and how great are our sins!