Psalms 119:123

...To prefigure His Cross, Moses by the merciful command of God raised aloft on a pole the image of a serpent in the desert, that the likeness of sinful flesh which must be crucified in Christ might be prefigured? By gazing upon this healing Cross, we cast out all the poison of the scandals of the proud: the Cross, which the Psalmist intently looking upon, saith, "My eyes have failed for Thy salvation, and for the words of Thy righteousness" (ver. 123). For God made Christ Himself "to be sin for us, on account of the likeness of sinful flesh, that we may be made the righteousness of God in Him." For His utterance of the righteousness of God he therefore saith that his eyes have failed, from gazing ardently and eagerly, while, remembering human infirmity, he longeth for divine grace in Christ.

The word - For the performance of thy faithful or merciful promise.

Mine eyes fail for that salvation,....

On the grounds of his integrity, desire for God's word, and covenant relation to Him, the servant of God may plead for His protecting care against the wicked, gracious guidance to the knowledge of truth, and His effective vindication of the righteous and their cause, which is also His own.

"Mine eyes fail for thy salvation." He wept, waited, and watched for God's saving hand, and these exercises tried the eyes of his faith till they were almost ready to give out. He looked to God alone, he looked eagerly, he looked long, he looked till his eyes ached. The mercy is, that if our eyes fail, God does not fail, nor do his eyes fail. Eyes are tender things, and so are our faith, hope and expectancy: the Lord will not try them above what they are able to bear. "And for the word of thy righteousness:" a word that would silence the unrighteous words of his oppressors. His eyes as well as his ears waited for the Lord's word: he looked to see the divine word come forth as a fiat for his deliverance. He was "waiting for the verdict"— the verdict of righteousness itself. How happy are we if we have righteousness on our side; for then that which is the sinners' terror is our hope, that which the proud dread is our expectation and desire. David left his reputation entirely in the Lord's hand, and was eager to be cleared by the word of the Judge rather than by any defence of his own. He knew that he had done right, and, therefore, instead of avoiding the supreme court, he begged for the sentence which he knew would work out his deliverance. He even watched with eager eyes for the judgment and the deliverance, the word of righteousness from God which meant salvation to himself.