Let their eyes be darkened, that they may not see, and bow down their back alway.

People's New Testament

11:10 Let their eyes be darkened. See Ps 69:23. Darkness shall come upon them because they love darkness rather than light.

Bow down their back. This implies a condition of bondage on account of their sins.

Jamieson-Fausset-Brown Bible Commentary

10. Let their eyes be darkened . and bow down their back alway-expressive either of the decrepitude, or of the servile condition, to come on the nation through the just judgment of God. The apostle's object in making these quotations is to show that what he had been compelled to say of the then condition and prospects of his nation was more than borne out by their own Scriptures. But, Secondly, God has not cast away His people finally. The illustration of this point extends, Ro 11:11-31.

Matthew Henry's Concise Commentary

11:1-10 There was a chosen remnant of believing Jews, who had righteousness and life by faith in Jesus Christ. These were kept according to the election of grace. If then this election was of grace, it could not be of works, either performed or foreseen. Every truly good disposition in a fallen creature must be the effect, therefore it cannot be the cause, of the grace of God bestowed on him. Salvation from the first to the last must be either of grace or of debt. These things are so directly contrary to each other that they cannot be blended together. God glorifies his grace by changing the hearts and tempers of the rebellious. How then should they wonder and praise him! The Jewish nation were as in a deep sleep, without knowledge of their danger, or concern about it; having no sense of their need of the Saviour, or of their being upon the borders of eternal ruin. David, having by the Spirit foretold the sufferings of Christ from his own people, the Jews, foretells the dreadful judgments of God upon them for it, Ps 69. This teaches us how to understand other prayers of David against his enemies; they are prophecies of the judgments of God, not expressions of his own anger. Divine curses will work long; and we have our eyes darkened, if we are bowed down in worldly-mindedness.