I have longed for thy salvation, O Jehovah! Although all men desire to be in happy circumstances, and no man avowedly repudiates God's favor; yet so confused and uncertain are the ideas which they entertain of that in which a life of happiness or propriety consists, that very few are to be found directing their aspirations to God. Some are carried away by their own ambition, some are wholly possessed with avarice, and others burn with lust, all imagining, that the farther they recede from God, everything will prosper so much the better with them. In short, in proportion as each man is desirous to be safe, in the same proportion does he provoke the anger of God, by seeking the means of his safety in all directions. The construction in the Hebrew text denotes steadfastness, or constancy of desire; for literally it is, that He Had longed for the salvation of God, and not that he only at the present time began to long for it. He next expresses the manner in which we are patiently to long for salvation; which is, by seeking consolation and relief in all our calamities from the word of God; for whoever does not comfort himself by a reliance on the grace promised in the word, will quail at the slightest assault made upon him. The Prophet then wisely kept his thoughts close upon the divine word, that he might not be turned away from hoping for the salvation of God.

I have longed for thy salvation, O Lord - See the notes at Psalm 119:166. The word rendered "I have longed" denotes an earnest desire or wish. Compare the notes at Psalm 42:1, and the notes at Psalm 119:20.
And thy law is my delight - It is so much the object of my delight that I earnestly long or desire to see more and more of its richness and fullness.

I have longed for thy salvation, O Lord,.... For temporal salvation and deliverance from enemies; and for spiritual and eternal salvation by the Messiah; and for the Messiah himself, the author of it: Kimchi interprets it of the salvation of the soul in the world to come; see Psalm 119:81;
and thy law is my delight; or "delights" (n); his exceeding great delight, as being pure and perfect, holy, just, and good; a transcript of the divine nature, a revelation of the divine will; as in the hands of Christ, his surety and Saviour, who had engaged to fulfil it for him; and as written in his heart; and as delivered from the curse and condemnation of it, through the suretyship engagements of Christ.
(n) "deliciae meae", Montanus, Tigurine version.