This passage is Yahweh’s endorsement on the prophet’s words and actions. There is no question that his call to preach comes from Yahweh. However, “prosperous” may be confusing, given its contemporary meaning of economic well-being. Victor Ludlow quotes the New King James Version of this passage: “Also, says the Lord; I the Lord I, I predicted and I called him to declare, I have brought him and he shall succeed in his mission.” Gileadi translates it: “I myself have spoken it, and also called him; I have brought him, and I will prosper his way.”
Each rendition emphasizes the ultimate success of the prophet’s spiritual goals, removing any possibility that the success might have been monetary.
Variant/Translation: The Book of Mormon adds a phrase to the beginning of this verse from the King James Version, which reads: “I, even I, have spoken; yea, I have called him.” The Book of Mormon addition clarifies the curt and perhaps difficult “I, even I” but without changing the meaning.
Similarly, the Book of Mormon adds, “I have called him to declare.” Again, this simply improves the English without altering the intent of the text. Tvedtnes notes that no other version of Isaiah makes a corresponding change.