Q. When Isaiah had his vision in the temple, who did he see? Was this a theophany of Jesus?
Actually, Isaiah’s vision would not be considered a theophany. That term means literally an “appearance of God” and it refers to those instances in the Old Testament when God, initially seeming to be human, appears to people and visits with them. The Bible often describes this human-like figure as the “angel of the Lord,” but sometimes the narrative shifts and it calls the figure “the Lord” (i.e. Yahweh, God Himself).
For example, in the story where Hagar flees from Sarah’s mistreatment, the text depicts the “angel of the Lord” speaking with Hagar. But at the end of the episode, it describes Hagar giving the name El-Roeh (“the God who sees”) to “the Lord who spoke to her.” Similarly, at the start of the story of the burning bush, the “angel of the Lord” appears to Moses in the flames. But the text then describes “the Lord” or “God” speaking to Moses from the bush.
When the angel of the Lord first appears to the future mother of Samson, she thinks he is a “man of God” (a prophet). When he returns, her husband asks him, “Are you the man who talked to my wife?” But eventually they both realize that he’s actually the the “angel of the Lord“—when he ascends to heaven on the flames of a fire they make to offer a sacrifice! Then the husband says, “We have seen God!”
So a theophany is an appearance of God on earth in human form, interacting with people who only eventually realize that He’s really God. Many Christian interpreters believe that these are actually appearances of the pre-incarnate Christ, that is, of Jesus in the human form that he would eventually have when he took on human flesh by being born to a human mother.
Isaiah’s vision in the temple is different. For one thing, there’s no question, right from the beginning, that Isaiah is seeing God. He says: “I saw the Lord, high and exalted, seated on a throne; and the train of his robe filled the temple. Above him were seraphim, each with six wings: With two wings they covered their faces, with two they covered their feet, and with two they were flying. And they were calling to one another: ‘Holy, holy, holy is the Lord Almighty; the whole earth is full of his glory.’ At the sound of their voices the doorposts and thresholds shook and the temple was filled with smoke.” So this is not a case in which God appears in human form. Rather, it’s a vision of the divine throne room, as Daniel would later have when he saw “thrones set in place, and the Ancient of Days took his seat. His clothing was as white as snow; the hair of his head was white like wool. His throne was flaming with fire, and its wheels were all ablaze. A river of fire was flowing, coming out from before him. Thousands upon thousands attended him; ten thousand times ten thousand stood before him.” John reports a similar vision of the heavenly throne room in the book of Revelation.
In addition, while the Lord interacts with Isaiah during the course of the vision (He asks, “Whom shall I send?” and Isaiah replies, “Send me!”), this isn’t a case where God actually comes to earth to visit and speak with a particular person. Other biblical figures interact similarly with characters in their own visions, but this is not the same thing as a theophany. And so we should conclude that Isaiah saw not the pre-incarnate Jesus, but the “Ancient of Days,” identified with God the Father, on the heavenly throne.