John Gill

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.