In the traditional Christian interpretation, Isaiah is writting about Jesus Christ.
According to Rashi and other Jewish commentators, Isaiah is writing about the remnant of Israel. The singular pronoun, according to this interpretation, is used as a collective plural. The English word, "seed", is used in this way. The form of the word is singular but can mean one or many. The interpretations do not have to be mutually exclusive.
Isaiah 53:2
Read Isaiah chapter 53.
The Romans were told and showed that he was the son of God, but chose not to believe it. Also, this was apart of God's plan. Throughout the first testament God slowly reveals his plan. Isaiah 7:14, Isaiah 8:6-8, Isaiah 11:10-12, Isaiah 16:5, Isaiah 53:3-6, and Isaiah 53:11.
Isaiah 53:7 and Acts 8:32
References to Jesus in the Old Testament can be found in prophecies and foreshadowing, such as in Isaiah 7:14 and Isaiah 53.
Isaiah 53:3 - This is referring to Jesus
Isaiah 53:4,5 Matt.8:17
References to Jesus Christ in the Old Testament can be found in prophecies and foreshadowing, such as in Isaiah 7:14 and Isaiah 53.
Because of Jesus' sacrificial role, John the Baptizer identified Jesus as "the Lamb of God that takes away the sin of the world. In speaking of Jesus as a Lamb, John may have had in mind the words of Isaiah: "He was being brought just like a lamb to the slaughtering." (Isaiah 53:7) "He poured out his soul to the very death," prophesied Isaiah. (Isaiah 53:12)
God foretold this via His prophets: See Isaiah 52:13 thru Isaiah 53 as an example.
Isaiah.
The Prophet Isaiah is attributed to writing only one book in the Canonized Bible (the bible with 66 Books and Old & New testament divisions), the Book of Isaiah.