We are always thankful when a Bible account lets us know the exact time that it occurred. That is the case here with Isaiah receiving his call in the year King Uzziah died, that we know to have been in 742 B.C..
With Biblical visions such as this one with which Isaiah was treated, the details of the vision, instead of being exact replicas of reality, are made to suit the preconceptions of the one receiving the vision. Here, Isaiah saw God in a heavenly temple because the Israelites believed Jerusalem’s temple, in all its dimensions, to be a replica of God’s temple in heaven.
Their word for “holy” actually meant “being completely different from us.”
Ancient peoples all believed that if they gazed on God that they would die immediately. Perhaps that belief can be traced to people worshipping the sun.