How Isaiah and other people in the Bible sees God, if God said to Moses "nobody can see Me without dying first"?
I would recommend Justin Martyr's "Dialog with Trypho" where he describes the relationship of God the Father, and God's Angel who appeared to the Prophets, and wrestled with Jacob.
I have found this book to be very fruitful in my understanding of the Trinity, and the relationship of the New Testament with the Old.
Trypho is a 2nd Century AD Jewish Philosopher that inquired about Justin's faith in Christ, and Justin was very thorough (and repetitive) in his answers, citing many examples of prophecy in the Old Testament that is fulfilled in Christ.
It's online and free to read - look up Early Church Fathers and that should pull it up.
Not exactly what God said to Moses. He didn’t say “you can’t see me until you die,” He said (in Ex. 33:20) “no one can see me and live,” in response to Moses request to see his “glory.” Yet back in chapter 24, Moses and 73 others went up and feasted in the presence of God, and it was worth remarking upon: “God did not raise up his hand,” against them, they saw God and lived. So what Moses was asking for was apparently something more awesome, more grand and glorified even than that experience he had already had, or the many times to come in which he “entered the Presence” and that, God said, would be too much for a mere mortal to survive.
Most readers, as far as I know, consider Isaiah 6 to be a vision, like Daniel’s in chap 7 of that book.