I don't think I'll be spending much time on this thread and, if you are interested, Judaism has a clear set of steps and expectations about repentance, but I just wanted to point out that if you start with a misunderstanding about Isaiah, you will come to mistaken conclusions.
The text does not say that Israel (or anyone) died to save humanity from sin. It says that other nations will, in the future, recognize that they only had peace through their oppressing of Jews and that the Jews, by suffering the sinful actions of their oppressors helped keep the world at peace for those oppressors.
I assume that you will choose to stick with your understanding of the chapter (though it isn't really a chapter, but a fluid continuation of an idea that begins verses earlier) so we will have little common ground to discuss.
Here's what Aish.com has to say about the Suffering Servant of Isaiah 53:
'Christianity claims that Isaiah 53 refers to Jesus, as the 'suffering servant'.
In actuality, Isaiah 53 directly follows the theme of chapter 52, describing the exile and redemption of the Jewish people. The prophecies are written in the singular form because the Jews ('Israel') are regarded as one unit. Throughout Jewish scripture, Israel is repeatedly called, in the singular, the 'Servant of God' (see Isaiah 43:8). In fact, Isaiah states no less than 11 times in the chapters prior to 53 that the servant of God is Israel.
When read correctly, Isaiah 53 clearly [and ironically] refers to the Jewish people being 'bruised, crushed and as sheep brought for the slaughter' at the hands of the nations of the world. These descriptions are used throughout Jewish scripture to graphically describe the suffering of the Jewish people (see Psalm 44).
Isaiah 53 concludes that when the Jewish people are redeemed, the nations will recognise and accept responsibility for the inordinate suffering and death of the Jews'.
Do you agree with this interpretation?