Why does it say "v'Atah Avinu Atah"?
Radak: Even though we sinned in front of You, we are Your children and You are our Father. A father does not abandon his son, even if he sinned against him.
Malbim: This is the end of the complaint that began "va'Yizkor Yemei Olam" (63:11). [Even] if we sinned via removing Your Shechinah from among us, You are our father - it is proper for a father to have mercy on his children!
Why does it say "Anachnu ha'Chomer v'Atah Yotzerenu"?
Radak: The potter changes the substance (clay) from Kli to Kli, as is proper in his eyes. If it is improper, he makes a different Kli. So we are in Your hands, but Nochrim are not. Your Hashgachah is not constantly on them. On us, You constantly pay for our deeds. If we sinned and You are angry at us, we are a broken Kli. Make us another Kli!
Malbim: We are like substance that can receive any form that the potter wants to put on it, like Yirmeyah said "hacha'Yotzer ha'Zeh Lo Uchal La'asos Lachem Beis Yisrael...; Rega Adaber...; v'Shav ha'Goy... v'Nichamti" (18:6-8). We are prepared to receive Musar and rebuke, if You will return Your Elokus on us.
Why did he add "u'Ma'ase Yadecha Kulanu"?
Malbim: A worker does not want to destroy what he made.
