The cup of salvation He refers to a custom which was prevalent under the Law. For when they rendered solemn thanks to God, a feast was also appointed, at which, in token of their gladness, there was an holy libation. This being a symbol of their deliverance from Egyptian thraldom, is for that reason here called the cup of salvation [1] The term to call upon, signifies to celebrate the name of God; and this he expresses more plainly, subsequently, by saying that he would pay his vows in the assembly of the faithful, the sanctuary alone being the place where sacrifices could be offered. The amount is, that the faithful need not be greatly perplexed about the way of performing their duties, God not demanding from them a return which he knows they are unable to give, but being satisfied with a bare and simple acknowledgment. The proper return is to own our obligation to him for every thing. If God deal so kindly and mercifully with us, and we fail in giving to him the tribute of praise for our deliverance which he claims, then our supineness becomes the more base. And certainly they are unworthy of the enjoyment, I say not of the riches of the world, but of the light of the sun and the air by which we breathe and live, who would rob the Author of them of the small return which so legitimately belongs to him. The Mosaic ritual has indeed been abrogated, and along with it the external libation referred to by David, yet the spiritual service, as we found in Psalm 50:23, "The sacrifice of praise shall glorify me," is still in force. Let us, however, bear in mind, that God is lawfully praised by us, when we offer in sacrifice not only our tongues, but also ourselves, and all that we possess. And this not because God derives any profit from it, but because it is reasonable that our gratitude should manifest itself in this way.

Footnotes

1 - That there is here an allusion to the cup of wine drunk in the offering of eucharistical sacrifices is very generally admitted by commentators. During the feast that followed these sacrifices, the master of the family took a cup of wine into his hands, and after solemnly giving thanks to God for the mercies experienced, first drank of it himself, and then delivered it to all present to be partaken of in rotation. "The cup here spoken of by the Psalmist," says Cresswell, "was probably used by the master of a Hebrew family at an entertainment in his own house, at which the remainder of the victims was eaten, after he had offered (Leviticus 7:11, etc.) the sacrifice of a peace-offering for a thanksgiving; when, lifting up the cup of wine in his hand, he called upon the name of the Lord, giving him thanks. The modern Jews are said to use a similar ceremony every year in commemoration of the deliverance of their ancestors from the bondage of Egypt." Some, indeed, deny that there is any allusion to such eucharistical sacrifices, as Hengstenberg, who observes, that this communion cup is a mere fiction. In the institution of the festival offerings, nothing is indeed said of the cup; but we know from Matthew 26:29, 30, that in the feast of the Passover, for instance, the drinking of a cup of wine and the singing of a hymn were parts of the observance. From Jewish tradition we also learn that such was the ancient practice. See Lightfoot's Horae Hebraicae on Matthew 26. Our Lord, apparently in imitation of the Jewish custom, as the head of the family, at the feast of the Passover, "took the cup, and gave thanks," (Luke 22:17.) In allusion to this custom, Paul calls the communion cup in the Lord's Supper "the cup of blessing," (1-Corinthians 10:16.) The Psalmist, then, here intimates his intention of publicly yielding thanks to God for the mercies bestowed upon him. There was a libation of wine enjoined by the Mosaic law to be made in the temple every morning and evening for a drink-offering, (Numbers 28:7,) to which some suppose there is here a reference, observing, that the three last verses seem to intimate, that the Psalmist was now at the temple, offering the meat-offering, drink-offering, and sacrifices, to the Lord.

I will take the cup of salvation - Compare the notes at Psalm 11:6. The "cup of salvation" means the cup by which his sense of the greatness of the salvation might be expressed - the cup of thanksgiving. Compare the notes at 1-Corinthians 10:16. The reference seems to be to a custom in festivals of drinking a cup of wine as a special expression of thanks or of obligation. The act would be more solemn, and the truth more deeply impressed on the mind, when accompanied by some religious rite - some ceremonial, as in the Lord's Supper, expressly designed to call the mercy of God to remembrance.
And call upon the name of the Lord - Engage in a solemn act of devotion; make it a matter of special ceremony or observance to call the mercy of God to remembrance. This was one way of rendering to the Lord a return for the benefits received at his hands; as it is now. Christians do this at the table of the Lord - in the observance of the Lord's Supper.

I will take the cup of salvation - Literally, The cup of salvation, or deliverance, will I lift up. Alluding to the action in taking the cup of blessing among the Jews, which, when the person or master of the family lifted up, he said these words, "Blessed be the Lord, the Maker of the world, who has created the fruit of the vine!"
But it may probably allude to the libation-offering, Numbers 28:7; for the three last verses seem to intimate that the psalmist was now at the temple, offering the meat-offering, drink-offering, and sacrifices to the Lord. Cup is often used by the Hebrews to denote plenty or abundance. So, the cup of trembling, an abundance of misery; the cup of salvation, an abundance of happiness.
And call upon the name of the Lord - I will invoke his name, that I may get more of the same blessings; for the only return that God requires is, that we ask for more. Who is like God? One reason why we should never more come to a fellow-mortal for a favor is, we have received so many already. A strong reason why we should claim the utmost salvation of God is, because we are already so much in debt to his mercy. Now this is the only way we have of discharging our debts to God; and yet, strange to tell, every such attempt to discharge the debt only serves to increase it! Yet, notwithstanding, the debtor and creditor are represented as both pleased, both profited, and both happy in each other! Reader, pray to him, invoke his name; receive the cup - accept the abundance of salvation which he has provided thee, that thou mayest love and serve him with a perfect heart.

I will (h) take the cup of salvation, and call upon the name of the LORD.
(h) In the Law they used to make a banquet when they gave solemn thanks to God, and to take the cup and drink in sign of thanksgiving.

I will take the cup of salvation,.... Or "salvations" (n); not the eucharistic cup, or the cup in the Lord's supper, which the apostle calls "the cup of blessing", 1-Corinthians 10:16; though some so think, and that the psalmist represents the saints under the Gospel dispensation; nor the cup of afflictions or martyrdom for the sake of Christ; being willing, under a sense of mercies received, to bear or suffer anything for his sake he should call him to; as knowing it would be a token to him of salvation, and work for his good: but rather an offering of praise for temporal salvation, and for spiritual and eternal salvation; in allusion to a master of a family, who at the close of a feast or meal, used to take up a cup in his hands, and give thanks; see Matthew 26:27;
and call upon the name of the Lord; invocation of the name of the Lord takes in all worship and service of him, public and private, external and internal; and particularly prayer, which is calling upon the Lord in the name of Christ, with faith and fervency, in sincerity and truth: and the sense of the psalmist is, that he would not only give thanks for the mercies he had received, but continue to pray to God for more; and this was all the return he was capable of making.
(n) "salutum", Pagninus, Montanus, Vatablus, Gejerus, Michaelis; "salvationum", Musculus.

the cup of salvation--the drink offering which was part of the thank offering (Numbers 15:3-5).