Therefore will I praise thee, O Jehovah! In this verse he teaches us that the blessings God had conferred upon him, of which he had spoken, are worthy of being celebrated with extraordinary and unusual praises, that the fame of them might reach even the heathen. There is in the words an implied contrast between the ordinary worship of God which the faithful were then accustomed to perform in the temple, and this thanksgiving of which David speaks, which could not be confined within so narrow limits. The meaning, therefore, is, O Lord, I will not only give thee thanks in the assembly of thy people, according to the ritual which thou hast appointed in thy law, but thy praises shall extend to a greater distance, even as thy grace towards me is worthy of being recounted through the whole world. Moreover, from these words we conclude that this passage contains a prophecy concerning the kingdom of Christ, which was to come. Unless the heathen had been allured into the fellowship of the chosen people, and united into one body with them, to praise God among them would have been to sing his praises among the deaf, which would have been foolish work and lost labor. Accordingly, Paul very properly and suitably proves from this text, that the calling of the Gentiles was not a thing which happened by chance, or at a venture, (Romans 15:9.) We shall afterwards see in many places that the Church is appointed to be the sacred dwelling-place for showing forth the praises of God. And, therefore, the name of God could not have been rightly and profitably celebrated elsewhere than in Judea, until the ears of the Gentiles were opened, which was done when God adopted them, and called them to himself by the gospel.

Therefore will I give thanks unto thee - Margin, confess. The Hebrew word - ידה yâdâh - in the form used here, means properly to profess, to confess, to acknowledge; then especially to acknowledge or recognize blessings and favors; in other words, to give thanks, to praise. The idea here is that he would make a public acknowledgment of those blessings which he had received; or that he would cause the remembrance of them to be celebrated among the nations.
Among the heathen - Among the nations. See the note at Psalm 18:43. The meaning here is, that he would cause these blessings to be remembered by making a record of them in this song of praise; a song that would be used not only in his own age and in his own country, but also among other nations, and in other times. He would do all in his power to make the knowledge of these favors, and these proofs of the existence of the true God, known abroad and transmitted to other times. The apostle Paul uses this language Romans 15:9 as expressing properly the fact that the knowledge of God was to be communicated to the "Gentiles:" "As it is written, For this cause will I confess to thee among the Gentiles." The word "heathen" or nations, in the passage before us, corresponds precisely with the meaning of the word Gentiles; and Paul has used the language of the psalm legitimately and properly as showing that it was a doctrine of the Old Testament that the truths of religion were not to be confined to the Jews, but were to be made known to other nations.
And sing praises unto thy name - Unto thee; the name often being used to denote the person. The meaning is, that he would cause the praises of God to be celebrated among foreign or pagan nations, as the result of what God had done for him. Far, probably, very far beyond what David anticipated when he penned this psalm, this has been done. The psalm itself has been chanted by million who were not in existence, and in lands of which the psalmist had no knowledge; and, connected as it has been with the other psalms in Christian worship, it has contributed in an eminent degree to extend the praises of God far in the earth, and to transmit the knowledge of him to generations as they succeeded one another. What David anticipated is, moreover, as yet only in the progress of fulfillment. Millions not yet born will make use of the psalm, as million have done before, as the medium of praise to God; and down to the most distant times this sacred song, in connection with the others in the Book of Psalm, will contribute to make God known in the earth, and to secure for him the praises of mankind.

WilI I give thanks unto thee - among the heathen - Quoted by St. Paul, Romans 15:9, to prove that the calling of the Gentiles was predicted, and that what then took place was the fulfillment of that prediction.
But there is a sense in which it applies particularly to David, well observed by Theodoret: "We see," says he, "evidently the fulfillment of this prophecy; for even to the present day David praises the Lord among the Gentiles by the mouth of true believers; seeing there is not a town, village, hamlet, country, nor even a desert, where Christians dwell, in which God is not praised by their singing the Psalm of David."

Therefore will (m) I give thanks unto thee, O LORD, among the heathen, and sing praises unto thy name.
(m) This prophecy belongs to the kingdom of Christ and calling of the Gentiles, as in (Romans 15:9).

Therefore will I give thanks unto thee, O Lord, among the Heathen,.... These words are cited by the apostle, in Romans 15:9; and applied to the conversion of the Gentiles, which is manifestly prophesied of in some preceding verses of this psalm: there it is rendered, "I will confess to thee among the Gentiles"; and designs not confession of sin, nor profession of the truth, but an acknowledgment of unworthiness, joined with thankfulness for mercies received; done in the most public manner, not only in the congregation of the righteous, but before the Heathen conquered by him; owning before them all, that the victories he had obtained over them were not to be ascribed to his arm and sword, but to the power of the Lord;
and sing praises unto thy name; which is comely for the saints to do, and which Jesus Christ himself did, in the great congregation of his disciples, and among the Gentiles, by his apostles, and others, on the account of the conversion of them.

Paul (Romans 15:9) quotes from this doxology to show that under the Old Testament economy, others than the Jews were regarded as subjects of that spiritual government of which David was head, and in which character his deliverances and victories were typical of the more illustrious triumphs of David's greater Son. The language of Psalm 18:50 justifies this view in its distinct allusion to the great promise (compare 2-Samuel 7:12). In all David's successes he saw the pledges of a fulfilment of that promise, and he mourned in all his adversities, not only in view of his personal suffering, but because he saw in them evidences of danger to the great interests which were committed to his keeping. It is in these aspects of his character that we are led properly to appreciate the importance attached to his sorrows and sufferings, his joys and successes.

(Hebrews.: 18:50-51) The praise of so blessed a God, who acts towards David as He has promised him, shall not be confined within the narrow limits of Israel. When God's anointed makes war with the sword upon the heathen, it is, in the end, the blessing of the knowledge of Jahve for which he opens up the way, and the salvation of Jahve, which he thus mediatorially helps on. Paul has a perfect right to quote Psalm 18:50 of this Psalm (Romans 15:9), together with Deuteronomy 32:43 and Psalm 117:1, as proof that salvation belongs to the Gentiles also, according to the divine purpose of mercy. What is said in Psalm 18:50 as the reason and matter of the praise that shall go forth beyond Israel, is an echo of the Messianic promises in 2-Samuel 7:12-16 which is perfectly reconcileable with the Davidic authorship of the Psalm, as Hitzig acknowledges. And Theodoret does not wrongly appeal to the closing words עד־עולם against the Jews. In whom, but in Christ, the son of David, has the fallen throne of David any lasting continuance, and in whom, but in Christ, has all that has been promised to the seed of David eternal truth and reality? The praise of Jahve, the God of David, His anointed, is, according to its ultimate import, a praising of the Father of Jesus Christ.

Heathen - David is here transported beyond himself, and speaks this in special relation to Christ who was to be his seed, and of whom he was an eminent type, and by whom alone this was done. And therefore this is justly applied to him, and to his calling of the Gentiles, Romans 15:9.