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Long before Rashi in the year 1000 the Jewish understanding of Isaiah 53 was that is speaks about the nation Israel. In the Midrash Rabba on Numbers it is clearly written that the suffering servant is Israel.
In the Talmud, finished around the year 500, in tractate Brachot 5A, it is written at least three times that the suffering servant is Israel.
The targum Jonathan ben Uzziel from the first century says in his comment on Isaiah 53 multiple times that the servant is Israel.
And there is of course the Christian father of the church, Origen, born in the year 185, who says that in a debate with wise Jews, they told him that the servant in Isaiah 53 is the nation Israel.
He says that in his book "Contra Celsus". That book can be found online here:
http://www.newadvent.org/fathers/0416.htm
Look in book 1, the end of chapter 54, and the beginning of 55, There Origen writes:
"But He was wounded for our sins, and bruised for our iniquities. The chastisement of our peace was upon Him; by His stripes we were healed. We all, like sheep, wandered from the way. A man wandered in his way, and the Lord delivered Him on account of our sins; and He, because of His evil treatment, opens not His mouth. As a sheep was He led to slaughter; and as a lamb before her shearer is dumb, so He opens not His mouth. In His humiliation His judgment was taken away. And who shall describe His generation? because His life is taken away from the earth; because of the iniquities of My people was He led unto death." Now I remember that, on one occasion, at a disputation held with certain Jews, who were reckoned wise men, I quoted these prophecies; to which my Jewish opponent replied, that these predictions bore reference to the whole people, regarded as one individual, and as being in a state of dispersion and suffering, in order that many proselytes might be gained, on account of the dispersion of the Jews among numerous heathen nations."
This is very clear, Origen, debating Jews, is told by these Jews who are considered wise men, that Isaiah 53 is about Israel.
So not the messiah, but ISRAEL.
In the very beginning of Christianity.
For what is going on in Isaiah 53, look here: https://tinyurl.com/53-Isaiah