How can Jews say that the suffering servant of Isaiah 53 refers to the Jewish people when not every aspect of this passage has been fulfilled by any individual Jew, including Jesus?
God deals with Israel in two ways. Singularly, with every individual and collectively, with the nation as a whole. Isaiah 53 is an overview of the historical encounter of collective national Israel with the nations of the world and God's rewards to the collective remnant of Israel for its faithfulness to His Torah. A day is coming when the nations of the world will, by virtue of the Israelite triumphs, become aware of God's special relationship to Israel. This will have the effect of causing, first, shock and disbelief, and then, an acknowledgment of the special rewards that God will grant Israel, as is described in the latter part of Isaiah 53.
What the prophet in this chapter describes refers to Israel as a whole, not every individual Israelite. Not every Jew will have to undergo every aspect of suffering to be worthy of eventually partaking in the rewards God promises. Indeed, not every Israelite has to be faultless because the suffering servant, Israel, as a people is innocent. If one is to insist, however, that Isaiah 53 refers to a specific person, that individual would personally have to accomplish all that is required of the suffering servant of the Lord. Failure to do so is automatic disqualification.
It should be clear to everyone that even if Isaiah 53 referred solely to the Messiah this would still not infer any support for the claim that it refers to Jesus. The fundamental theological Questions raised by the missionaries are "Who is the Messiah?" and "If not Jesus, who then is the Messiah and when will he come?" Jews are not obligated to identify who the Messiah will be or give a timetable for his arrival. One can only discuss the case presented for past claimants to the title. On this basis, Jews can confidently say that Jesus is not the Messiah of Israel prophesied in the Hebrew Scriptures. Jesus could not be the Messiah by virtue of any one of a number of disqualifications. They range from not having the biblical genealogical criteria for that office (one would have to be a biological descendant of David through the male line of Solomon) to bringing about the very fundamentals of the messianic age as delineated in Isaiah, chapter 11.