Though this is an older thread, the subject is of interest to me.
Chapter 12 of John includes citations from both Isaiah chapter 6 (Isaiah's calling) and chapter 53 (the fourth 'Servant Song' often referred to as the 'Suffering Servant').
After quoting verses from both of these chapters in Isaiah (comp. John 12:38 with Isaiah 53:1; comp. John 12:39-40 with Isaiah 6:10), John 12:41 summarizes:
"These things said Isaiah, when he saw his glory, and spoke of him."
I think that John intended his readers to pay attention to the context of both the above verses from Isaiah while thinking through John's summary in 12:41. Earlier in this thread there is some acknowledgement that Isaiah made reference to "the King, Yahweh" (see Isa. 6:5). This thread also includes a claim that Isaiah's vision of the Lord (Isa. 6:1) is distinguished from seeing the glory of Christ (cf. John 17:5). For those who understand the Servant of Isaiah 52:13ff as Christ such a claim is probably necessary in order to maintain a theological position that views Christ as less than God.
One textual link in Isaiah that I didn't see referred to in the thread is a brief phrase that both Isaiah's calling (chapter 6) and Isaiah's fourth Servant Song (52:13-53:12) share in common. Both portions of Isaiah draw into focus one who is "high and lifted up" (Isaiah 6--"the Lord" [v. 1]; Isaiah 52:13--"my servant").
Isaiah 6 states:
"In the year that king Uzziah died I saw the Lord sitting upon a throne, high and lifted up, and his train filled the temple" (v. 1).
[It may help to bear in mind that seraphim were present on this occasion crying, "Holy, holy, holy is Yahweh of hosts--all the earth is filled with his glory" (v. 3).]
Isaiah 52:13 states:
"Behold, my servant will deal wisely, he will be high and lifted up and greatly exalted."
The difference between Isaiah's phrases is merely one of tense. Isaiah 6:1 employs a perfect tense (i.e. he was "high and lifted up"--רָם וְנִשָּׂא) while 52:13 uses the imperfect form (i.e. "he will be high and lifted up"--יָרוּם וְנִשָּׂא). Isaiah 6 refers back to Isaiah's vision which took place in the past, while Isaiah 52:13 anticipates the coming of the suffering "servant". John looks back at both the vision/calling of Isaiah as well as the prophecy of the servant.
[The Hebrew text might not be John's source as it looks like John (and Paul--cf. Rom. 10:16) draws his citation of Isaiah 52:13 from the Septuagint (or a parent text for the Septuagint). This appears to be the case as both John and Paul include the word "Lord" as the subject of their citations (i.e. "Lord, who hath believed our report?"); a feature not present in the Hebrew MT. Concepts of being "lifted up" and "glorified" are frequently referred to in John 12. The verbs match the Septuagint's rendering of Isaiah 52:13.]
Meanwhile, John appears to link the vision of Isaiah 6 with the prophecy of the servant in Isaiah 52:13ff. The idea of John referring to some glory that is less than Yahweh's glory seems to strive against the plain statement of Isaiah 6:3 which expressly refers to Yahweh and his glory that fills the earth. (Strange as it may seem, even Jewish mystical tradition of the medieval era cited this verse in a work called the Zohar with reference to God as in some sense a triad.
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Again, John 12:41 reads:
"These things said Isaiah, when he saw his glory, and spoke of him."
Unless John intended to confuse or mislead his readers, he chose a counter-intuitive way to focus on a measure of 'glory' that belongs to Christ as distinct from Yahweh. Isaiah 6:1-5 draws the glory of Yahweh into focus, vv. 6-12 elaborate on Isaiah's calling, v. 13 makes reference to the holy seed. John quoted v. 10 immediately before making his statement about Isaiah seeing "his glory" and speaking "of him" (12:41). By drawing a link with the servant of Isaiah 53, John appears to highlight a paradox in the relationship between the glory of Christ's sufferings and the vision of Yahweh's glory. John may intend to convey a similar message via Revelation chapters 4 and 5 by describing the four beasts with six wings (like the seraphs of Isaiah) who also cry out, "Holy, holy, holy" (4:8) which seems to reach a crescendo as both the one on the throne and the Lamb become the objects of their worship (5:11-14).
Peace in Christ...
Stevend