For this reason
This phrase indicates a causal relationship, pointing back to the preceding verses where John discusses the unbelief of the people despite witnessing Jesus' miracles. The Greek phrase "διὰ τοῦτο" (dia touto) suggests a divine purpose or plan. In the broader scriptural context, it emphasizes the sovereignty of God in the unfolding of His redemptive plan. Historically, this reflects the Jewish expectation of signs and wonders as validation of divine authority, yet their hearts remained hardened.

they were unable to believe
The Greek word "δύναμαι" (dynamai) means "to be able" or "to have power." Here, it is used in the negative, indicating an inability. This inability is not merely intellectual but spiritual, highlighting the condition of the human heart apart from divine intervention. Theologically, this speaks to the doctrine of total depravity, where sin affects every part of human nature, rendering individuals incapable of coming to faith without God's grace.

because Isaiah
Isaiah, the prophet, is frequently quoted in the New Testament, especially in relation to the Messiah. His writings are foundational for understanding the messianic prophecies and the spiritual condition of Israel. The reference to Isaiah here underscores the continuity of God's revelation and the fulfillment of prophecy in Jesus Christ. Historically, Isaiah's ministry occurred during a time of great political turmoil, yet his prophecies pointed to a future hope and redemption.

said again
The word "again" indicates that this is not the first time Isaiah's words are being referenced. It suggests a pattern or recurring theme in Isaiah's prophecies concerning the hardness of heart and the rejection of God's message. This repetition serves to reinforce the authority and reliability of Scripture, as well as the persistent nature of unbelief throughout history.

(39) Therefore they could not believe, because.--The words refer to those which have gone before, not to those which follow, and then by an addition give the reason more fully. "It was on account of the divine will expressed in Isaiah's prophecy." "It was therefore, namely, because Isaiah said again."

The words, "they could not believe," must be taken in their plain meaning as expressing impossibility. The Apostle is looking back upon the national rejection of Christ, and seeks a reason for it. He remembers how our Lord Himself had explained His method of teaching by parables, and has based it upon this prophecy of Isaiah (Matthew 13:14). The principle was that which has been repeated in His last public words (John 12:35-36); that power used is increased, and power neglected destroys itself. Here, then, in these prophetic words was the reason they could not believe. Wilful rejection had been followed by rejection which was no longer within the power of the will. With this statement of St. John's should be compared our Lord's words on the same subject in John 5:40; John 6:37, Notes, and St. Paul's arguments in Romans 9-11.

Verses 39, 40. - In these verses, however, a deeper difficulty still is involved. The διὰ τοῦτο... ὅτι leave us no option (see John 7:21, 22) but to translate: For from this reason they were unable to believe (see other illustrations of the usage, John 5:18; John 8:47; John 10:17). There was a moral impossibility inherited by them through ages of rebellion and insensibility to Divine grace, and through their misuse of Divine revelation. The issue of it was, "'they could not believe." Because Isaiah said again; i.e. in another place; illustrative of this great Messianic oracle and the reception it would meet with from the nation as a whole. In the passage which follows we have a translation which does not directly correspond with either the Hebrew or the LXX. of Isaiah 6:9, 10. The prophet is bidden by the Lord to punish the people for their obduracy by blinding their eyes and hardening their heart, and even arresting the conversion and healing of the covenant people. This same solemn passage is quoted in four other places in the New Testament. Perhaps Luke 8:10 is hardly to be regarded as a citation; a small portion only of the passage is introduced from the prophet without reference to him, and this is inverted in order. In Matthew 13:14, 15 there is the nearer approach to the LXX., which, however, transforms the שִׁמְעוּ שָׁמוםע, "to hear, hear ye," into ἀκοῇ ἀκούσετε, "by hearing ye shall hear;" and similarly with the other clauses, - the imperative of God's command to the prophet being resolved into the future of most certain accomplishment, and in place of "Lest they understand with their heart, and convert, and he [God] heal them," LXX. reads, "Lest... should convert, and I [who give you the command to deliver such a message, notwithstanding its results upon them] heal them." This St. Matthew has followed. Mark 4:12 has given a different representation again, and, while omitting a considerable portion of the passage, passes to the climax, which is put thus: "Lest they should be converted, and their sin should be forgiven them," showing that the evangelist, looking to the Hebrew rather than to the LXX., has resolved its meaning into a clearly related paraphrase. In Acts 28:26, 27 the passage almost verbally follows the LXX. Here in the remarks of St. John the whole passage seems independent of the LXX., and to have resolved the Hebrew "imperative," addressed to the prophet, into an awful assurance of Divine agency in the matter. Instead of "shut their eyes," Hebrew imperative, or LXX. "their eyes they closed," ἐκάμμυσαν, LXX., he says, τετύφλωκεν, He hath blinded their eyes; and so with the other terms: He hardened their heart; in order that they should not (lest they should) see with their eyes, and perceive with their heart, and should turn, and I should heal them. In ἰάσωμαι the evangelist, returning to the first person, draws a distinction between the retributive activity of the pre-existent Christ of the earlier revelation and the historical Savior. There is no slip or negligence. Godet and Hengstenberg go a long way in making God the Author of the sin and rejection, and the cause of the impossibility of their repentance and healing. That which in all the several quotations of this passage we learn from Isaiah's oracle is that the unforced and willful rejection of the Divine Word is visited by condign withdrawment of the faculty to receive even more accessible and apprehensible truth. This is the great law of Divine operation in the nature of all moral beings. This law is described as a distinctly foreseen event, and by LXX. as an apprehensible and even conspicuous fact, and it is quoted by St. John as the direct consequence of the Divine activity. He does not mean to say that, because Isaiah foretold this as a Divine reprobation, they, whether they would or not as individuals, were fated to die the death of blindness, but they could not believe, because, on the principle involved in Isaiah's predictions, the Divine government had fulfilled itself, had acted upon its universal law, and in consequence of vows and acts of willful disobedience, they had thus fallen into the curse that belongs to a neglect of the Divine. "They could not believe." Thus even now disinclination to God and to righteousness leads to moral incapacity. Sin is punished by its natural consequences: unbelief is punished by unsusceptibility to clearest evidence; prejudice by blindness; rejection of Divine love by inability to see it at its best. How is this natural evolution brought about? Surely by laws of God. What are these laws but God's ways of acting with all moral agents whatever?

Parallel Commentaries ...


For this reason
Διὰ (Dia)
Preposition
Strong's 1223: A primary preposition denoting the channel of an act; through.

they were unable
ἠδύναντο (ēdynanto)
Verb - Imperfect Indicative Middle or Passive - 3rd Person Plural
Strong's 1410: (a) I am powerful, have (the) power, (b) I am able, I can. Of uncertain affinity; to be able or possible.

to believe.
πιστεύειν (pisteuein)
Verb - Present Infinitive Active
Strong's 4100: From pistis; to have faith, i.e. Credit; by implication, to entrust.

For
ὅτι (hoti)
Conjunction
Strong's 3754: Neuter of hostis as conjunction; demonstrative, that; causative, because.

again,
πάλιν (palin)
Adverb
Strong's 3825: Probably from the same as pale; anew, i.e. back, once more, or furthermore or on the other hand.

Isaiah
Ἠσαΐας (Ēsaias)
Noun - Nominative Masculine Singular
Strong's 2268: Isaiah, the prophet. Of Hebrew origin; Hesaias, an Israelite.

says:
εἶπεν (eipen)
Verb - Aorist Indicative Active - 3rd Person Singular
Strong's 2036: Answer, bid, bring word, command. A primary verb; to speak or say.


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NT Gospels: John 12:39 For this cause they couldn't believe (Jhn Jo Jn)