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. And in this way he explained the words, “Your form shall be of no reputation among men;” and then, “They to whom no message was sent respecting him shall see;” and the expression, “A man under suffering.”
Many arguments were employed on that occasion during the discussion to prove that these predictions regarding one particular person were not rightly applied by them to the whole nation. And I asked to what character the expression would be appropriate, “This man bears our sins, and suffers pain on our behalf;” and this, “But He was wounded for our sins, and bruised for our iniquities;” and to whom the expression properly belonged, “By His stripes were we healed.” For it is manifest that it is they who had been sinners, and had been healed by the Saviour's sufferings (whether belonging to the Jewish nation or converts from the Gentiles), who use such language in the writings of the prophet who foresaw these events, and who, under the influence of the Holy Spirit, applied these words to a person.
But we seemed to press them hardest with the expression, “Because of the iniquities of My people was He led away unto death.” For if the people, according to them, are the subject of the prophecy, how is the man said to be led away to death because of the iniquities of the people of God, unless he be a different person from that people of God? And who is this person save Jesus Christ, by whose stripes they who believe in Him are healed, when “He had spoiled the principalities and powers (that were over us), and had made a show of them openly on His cross?” At another time we may explain the several parts of the prophecy, leaving none of them unexamined.
But these matters have been treated at greater length, necessarily as I think, on account of the language of the Jew, as quoted in the work of Celsus.
Source: Against Celsus (New Advent)