The righteousness of thy testimonies endureth forever. The Psalmist repeats what he had already before stated, that there is a great dissimilarity between the righteousness of God's testimonies and man's inventions; the splendor of the last quickly vanishing away, whereas the other continues steadfast for ever. He repeats this twice; for although the world is forced to attribute the praise of righteousness to the law of God, yet the majority of mankind are carried away after their own speculations, so that there is nothing more difficult than to hold us fast in our obedience to God. David's drift is to show that everlasting righteousness is not comprehended elsewhere than in God's law, and that it is in vain to seek for it anywhere else; and there is accordingly here laid down a clearer definition of righteousness, which is, that righteousness consists in our keeping ourselves within the bounds of the law. As to the last clause of the verse, Give me understanding and I shall live, I read it in connection with the preceding clause; for although David desires to have his mind enlightened by God, yet he does not conceive of any other way by which he was to obtain an enlightened understanding than by his profiting aright in the study of the law. Farther, he here teaches, that men cannot, properly speaking, be said to live when they are destitute of the light of heavenly wisdom; and as the end for which men are created is not that, like swine or asses, they may stuff their bellies, but that they may exercise themselves in the knowledge and service of God, when they turn away from such employment, their life is worse than a thousand deaths. David therefore protests that for him to live was not merely to be fed with meat and drink, and to enjoy earthly comforts, but to aspire after a better life, which he could not do save under the guidance of faith. This is a very necessary warning; for although it is universally acknowledged that man is born with this distinction, that he excels the lower animals in intelligence, yet the great bulk of mankind, as if with deliberate purpose: stifle whatever light God pours into their understandings. I indeed admit that all men desire to be sharp-witted; but how few aspire to heaven, and consider that the fear of,God is the beginning of wisdom. Since then meditation upon the celestial life is buried by earthly cares, men do nothing else than plunge into the grave, so that while living to the world, they die to God. Under the term life, however, as I have elsewhere said, the Prophet denotes the utmost he could wish. Lord, as if he had said, although I am already dead, yet if thou art pleased to illumine my mind with the knowledge of heavenly truth, this grace alone will be sufficient to revive me.

The righteousness of thy testimonies - The principles of righteousness on which they are founded. Those testimonies - those laws - are not arbitrary, or the mere expressions of will. They are founded on right and justice as seen by God, and his laws are his testimony as to what truth and justice are.
Is everlasting - See the notes at Psalm 119:142.
Give me understanding, and I shall live - Give me a right view of thy law, and thy truth, and I shall have real life. See the notes at Psalm 119:34.

The righteousness of thy testimonies is everlasting - Thy moral law was not made for one people, or for one particular time; it is as imperishable as thy nature, and of endless obligation. It is that law by which all the children of Adam shall be Judged.
Give me understanding - To know and practice it.
And I shall live - Shall glorify thee, and live eternally; not for the merit of having done it, but because thou didst fulfill the work of the law in my heart, having saved me from condemnation by it.

The righteousness of thy testimonies [is] everlasting: give me understanding, and I shall (d) live.
(d) So that the life of man without the knowledge of God is death.

The righteousness of thy testimonies is everlasting,.... Or, "for ever" (b). The righteousness which they require, or which they publish; the righteousness revealed in the Gospel, which is the righteousness of Christ; See Gill on Psalm 119:142;
give me understanding, and I shall live; an understanding of the testimonies of the Lord, of the word of God, the law of God, and Gospel of Christ; an understanding of divine and spiritual things; a clearer and larger understanding of them, which is the gift of God; both that itself at first, and an increase of it here prayed for, the end, issue, and effect of which is life. Such live spiritually, and by faith; they live cheerfully and comfortably, and "for ever", as Aben Ezra and Kimchi repeat from the former clause: for "this is life eternal know the only true God and Jesus Christ"; or to have spiritual understanding of them, and of those things which relate to spiritual peace and comfort here, and eternal happiness hereafter, John 17:3.
(b) "in seculum", Pagninus, Montanus, Junius & Tremellius, Piscator, Cocceius; "in aeternum", V. L.