You do realize that:
1) Isaiah was written by several human being
2) These people all lived in a time before Jesus, and before his system of salvation was known.
3) Isaiah was written as a Judaic prophecy. That’s its trajectory. The Jews are still waiting for its fulfillment.
4) to appropriate another religion’s texts and claim they mean what you want them to mean, does not change the fact that it’s not what the authors meant, and it’s the lowest form of treatment of the texts.
I do not 'realize' what you say in fact have some points of disagreement
1) Isaiah was a thus says the Lord through a specific named person.
If you examine Isaiah, it starts saying who Isiah is and in the second half only says 'thus says the Lord' (in chapters 40 on) It mentions a specific Isaiah son of and no one else... so I don't agree and the ordinary sense of the literature would not either. Chapter 40 starts a new column but.... it's like a second part but all sections are tied together interweaving the same melodies and countermelodies from the start
2) God sees the end from the beginning and says so in Isaiah But in the text Israel goes from unholy and rebellious to holy at the end, through the work of the servant in the servant songs and then the fruit of the servant seen in the servants (plural) songs.
3) Isaiah promised salvation to the gentiles and in Isaiah 6 through 53 there is described a hardening of the Jews 'who would believe our report' and so God mostly is saving gentiles 'to make Jews jealous' and eventually to save more in large numbers as the nations are blessed in the seed of Abraham who is Jesus
4) the Author was God. By another's text I think you mean my religion's text? My God, my saviour and in the end of Isaiah which breaks into marriage language points to the marriage supper of the Lamb