on John 12 :39
Therefore they could not believe - Why? Because they did not believe the report of the prophets concerning Christ; therefore they credited not the miracles which he wrought as a proof that he was the person foretold by the prophets, and promised to their fathers. Having thus resisted the report of the prophets, and the evidence of Christ's own miracles, God gave them up to the darkness and hardness of their own hearts, so that they continued to reject every overture of Divine mercy; and God refused to heal their national wound, but, on the contrary, commissioned the Romans against them, so that their political existence was totally destroyed.
The prophecy of Isaiah was neither the cause nor the motive of their unbelief: it was a simple prediction, which imposed no necessity on them to resist the offers of mercy. They might have believed, notwithstanding the prediction, for such kinds of prophecies always include a tacit condition; they may believe, if they properly use the light and power which God has given them. Such prophecies also are of a general application - they will always suit somebody, for in every age persons will be found who resist the grace and Spirit of God like these disobedient Jews. However, it appears that this prediction belonged especially to these rejecters and crucifiers of Christ; and if the prophecy was infallible in its execution, with respect to them, it was not because of the prediction that they continued in unbelief, but because of their own voluntary obstinacy; and God foreseeing this, foretold it by the prophet. Should I say that, they could not believe, means, they would not believe, I should perhaps offend a generation of his children; and yet I am pretty certain the words should be so understood. However, that I may put myself under cover from all suspicion of perverting the meaning of a text which seems to some to be spoken in favor of that awful doctrine of unconditional reprobation, the very father of it shall interpret the text for me. Thus then saith St. Augustin: Quare autem non Poterant, si a me quaeratur, cito respondeo; Quia Nolebant: Malam quippe eorum Voluntatem praevidit Deus, et per prophetam praenunciavit. "If I be asked why they Could not believe? I immediately answer, Because They Would Not. And God, having foreseen their Bad Will, foretold it by the prophet." Aug. Tract. 53, in Joan.
on John 12 :39
They could not believe - See Mark 6:5; "He could there do no mighty works," etc. The works can and could are often used in the Bible to denote the existence of such obstacles as to make a result certain, or as affirming that while one thing exists another thing cannot follow. Thus, John 5:44; "How can ye believe which receive honor one of another." That is, while this propensity to seek for honor exists, it will effectually prevent your believing. Thus Genesis 37:4 it is said of the brethren of Joseph that they "could not speak peaceably unto him." That is, while their hatred continued so strong, the other result would follow. See also Matthew 12:34; Romans 8:7; John 6:60; Amos 3:3. In this case it means that there was some obstacle or difficulty that made it certain that while it existed they would not believe. What that was is stated in the next verse; and while that blindness of mind and that hardness of heart existed, it was impossible that they should believe, for the two things were incompatible. But this determines nothing about their power of removing that blindness, or of yielding their heart to the gospel. It simply affirms that while one exists the other cannot follow. Chrysostom and Augustine understand this of a moral inability, and not of any natural want. of power. "They could not, because they would not" (Chrysostom in loco). So on Jeremiah 13:23, "Can the Ethiopian change his skin," etc., he says, "he does not say if is impossible for a wicked man to do well, but, because "they will not, therefore they cannot." Augustine says on this place: "If I be asked why they could not believe, I answer without hesitation, because they would not: because God foresaw their evil will, and he announced it beforehand by the prophet."
Said again - Isaiah 6:9-10.
on John 12 :39
12:39 Therefore now they could not believe - That is, by the just judgment of God, for their obstinacy and wilful resistance of the truth, they were at length so left to the hardness of their hearts, that neither the miracles nor doctrines of our Lord could make any impression upon them.