What is the meaning of "Im Shachachnu Shem Elokeinu"?
Radak: Did we think in our hearts 'the Goyim who afflict us do not believe in our G-d, and they are serene, and we who believe are afflicted. Let us forget Him, and revert to their gods!'? (Verse 22 says that Hashem knows that we did not.)
Malbim: Even though we spread our hands to a foreign god, we were forced. We did so only in action, but at the time our hearts were complete with Hashem's unity and Emunah in Him 1 .
One must be Moser Nefesh to avoid doing actions of idolatry, even if his heart does not accept the idolatry at all (YD 157:1)! If their hearts were complete with Hashem's Emunah, why did they spread their hands?! (PF)
Why does it say "va'Nifros Kapeinu l'El Zar"?
Radak: This is even when we were forced. Since we did not forget You in our hearts, how would we spread our hands to a foreign god?! We were Moser Nefesh to be killed, and not do so - "Ki Alecha Horagnu Chol ha'Yom" (verse 23).
Malbim: Refer to 44:21:1:2 and the note there.