For I knew that thou art stubborn, and thy neck is as an iron sinew, and thy forehead as brass.

From my knowing that thou art obstinate, And a sinew of iron thy neck, And thy forehead brass,

Because I saw that your heart was hard, and that your neck was an iron cord, and your brow brass;

Because I knew that you are obstinate, and your neck is an iron sinew, and your brow bronze;

For I knew that you are stubborn, and that your neck is like an iron sinew, and that your forehead is like brass.

Quia cognovi qubd durus sis, et nervus ferreus cervix tua, et frons tuae aenea.

For I knew that thou art obstinate. Literally it is, "On account of my knowing," or, "From nay knowing." Here the Lord solemnly declares by the Prophet, that it was on account of the hard-heartedness of the people that he spake of future events; as if he had said that he acted more liberally towards them than he ought to have done. Not that this was the only end which he aimed at; for we know that the chief use of doctrine belongs to believers, who gently submit themselves and cheerfully obey; but Isaiah, who had to deal with obstinate men, justly says that, if their depravity had not been incurable, God made use of an excellent remedy, by uttering many successive predictions for the purpose of ratifying his Law. Thus as he had foretold future events to the fathers, so he shews that he follows the same course, in order to conquer or soften the obstinacy and hard-heartedness of the people. And thy neck is an iron sinew, and thy forehead is of brass. He calls their neck "an iron sinew," because it cannot be bent. "Sinews" are indeed hard, but still they are capable of being bent; here, he says, there is no bending, because they are untameable. He next mentions "a brazen forehead," to denote their impudence. There are two ways by which we may be kept in the path of duty; first, if we are submissive and obey good instructions or holy commandments; and secondly, if, after having fallen into any sin, we are moved by sincere shame to repent of what we have done. When these are wanting, it is a sign of desperate wickedness. These are two proofs, therefore, which he has brought forward to shew that the nation was abandoned to everything that was sinful; they were refractory, and they were impudent. And yet, when the Lord cannot cure us in any other way, he treats even our perversity with such forbearance, that he is pleased to give us warning of future events. Thus he assumes, as it were, every possible shape, in order to recall us to himself, and bring us back into the right path.

Because I knew that thou art obstinate - I made these frequent predictions, and fulfilled them in this striking manner, because I knew that as a people, you were prone to unbelief, and in order that you might have the most full and undoubted demonstration of the truth of what was declared. As they were disinclined to credit his promises, and as he saw that in their long captivity they would be prone to disbelieve what he had said respecting their deliverance under Cyrus, he had, therefore, given them these numerous evidences of the certainty of the fulfillment of all his prophecies, in order that their minds might credit what he said about their return to their own land.
That thou art obstinate - Margin, as Hebrew, 'Hard,' The sense is, that they were obstinate and intractable - an expression probably taken from a bullock which refuses to receive the yoke. The word hard, as expressive of obstinacy, is often combined with others. Thus, in Exodus 32:9; Exodus 34:9, 'hard of neck,' that is, stiff-necked, stubborn; 'hard of face' Ezekiel 2:4; 'hard of heart' Ezekiel 3:7. The idea is, that they were, as a people, obstinate, rebellious, and indisposed to submit to the laws of God - a charge which is often brought against them by the sacred writers, and which is abundantly verified by all their history as a people (compare Exodus 32:9; Exodus 33:3-5; Exodus 34:9; Deuteronomy 9:6-13; Deuteronomy 31:27; 2-Chronicles 30:8; Ezekiel 2:4; Acts 7:51).
Thy neck is an iron sinew - The word גיד giyd means properly a cord, thong, or band; then a nerve, sinew, muscle, or tendon. The metaphor is taken from oxen when they make their neck stiff, and refuse to submit it to the yoke.
And thy brow brass - Thy forehead is hard and insensible as brass. The phrase is applied to the shameless brow of a harloi Jeremiah 3:3; Ezekiel 3:7, where there is an utter want of modesty, and consummate impudence. A brow of brass is an image of insensibility, or obstinacy (so in Jeremiah 6:28).

Because I knew that (e) thou [art] obstinate, and thy neck [is] an iron sinew, and thy brow brass;
(e) I have done for you more than I promised, that your stubbornness and impudency might have been overcome.

Because I knew that thou art obstinate,.... Or "hard" (a), hard hearted, an obdurate and rebellious people, contradicting and gainsaying:
and thy neck is as an iron sinew; stiffnecked, inflexible, not compliant with the will of God, and his commands; unwilling to admit his yoke, and bear it:
and thy brow brass; impudent, not ashamed of sin, nor blushing at it, refusing to receive correction for it, having a whore's forehead. This the Lord knew and foreknew, and therefore declared before hand what would come to pass unto them; who otherwise would have had the assurance to have ascribed them to themselves, or their idols, and not to him.
(a) "quod durus tu es", Pagninus, Montanus; "te durum esse", Junius & Tremellius, Piscator, Vitringa.

obstinate--Hebrew, "hard" (Deuteronomy 9:27; Ezekiel 3:7, Margin).
iron sinew--inflexible (Acts 7:51).
brow brass--shameless as a harlot (see Jeremiah 6:28; Jeremiah 3:3; Ezekiel 3:7, Margin).

I knew - Therefore I gave thee clearer demonstrations of my nature and providence, because I knew thou wast an unbelieving nation. Thy neck - Will not bow down to receive my yoke. Thy brow - Thou wast impudent.