(4, 5) The general sense of these verses is plain, though there are slightly different ways of understanding the expressions. The psalmist imagines that the word or promise, which has been so abundantly fulfilled, will, by its performance, convince all the kings of the earth, and bring them in confession and praise to Jehovah. For a Hebrew the expression “hear the words of Thy mouth,” referring in this instance immediately back to Psalm 138:2, was synonymous with “see Thy wonders,” since for them “God spoke and it was done.”

Psalm 138:4-5. All the kings of the earth shall praise thee — All the neighbouring kings; or, rather, this is a prophecy of the calling of the Gentiles, and so the generality of the kings of the earth are intended, according to the prediction, Psalm 72:11; All kings shall fall down before him, all nations shall serve him; when they shall hear the words of thy mouth — The gospel preached among them. Yea, they shall sing in the ways — Or, of, or, because of the ways, of the Lord; that is, his wonderful counsel and gracious providences toward themselves and others. For great is — Or, great shall be, the glory of the Lord — At that time the worship and glory of God shall not be confined to one small land, as now it is, but shall be extended to all parts of the world.

138:1-5 When we can praise God with our whole heart, we need not be unwilling for the whole world to witness our gratitude and joy in him. Those who rely on his loving-kindness and truth through Jesus Christ, will ever find him faithful to his word. If he spared not his own Son, how shall he not with him freely give us all things? If God gives us strength in our souls, to bear the burdens, resist the temptations, and to do the duties of an afflicted state, if he strengthens us to keep hold of himself by faith, and to wait with patience for the event, we are bound to be thankful.All the kings of the earth shall praise thee ... - That is, kings, princes, and rulers shall learn the words of promise; shall be made acquainted with the words which thou hast graciously spoken, and with their fulfillment, and shall be led to praise thee. This refers to a time, of which frequent prophetic mention is made in the Scriptures, when kings and rulers shall be converted to the true religion, and when they shall act an important part, by their example and influence, in maintaining and diffusing it. Compare Psalm 68:31-32; Isaiah 49:23. 3-5. That promise, as an answer to his prayers in distress, revived and strengthened his faith; and, as the basis of other revelations of the Messiah, it will be the occasion of praise by all who hear and receive it (Ps 68:29, 31; Isa 4:3).4 All the kings of the earth shall praise thee, O Lord, when they hear the words of thy mouth.

5 Yea, they shall sing in the ways of the Lord: for great is the glory of the Lord.

Psalm 138:4

"All the kings of the earth shall praise thee, O Lord, when they hear the words of thy mouth." Kings have usually small care to hear the word of the Lord; but King David feels assured that if they do hear it they will feel its power. A little piety goes a long way in courts; but brighter days are coming, in which rulers will become hearers and worshippers: may the advent of such happy times be hastened. What an assembly Ira "all the kings of the earth!" What a purpose! Gathered to hear the words of Jehovah's mouth. What a preacher! David himself rehearses the words of Jehovah. What praise I when they all in happy union lift up their songs unto the Lord. Kings are as gods below, and they do well when they worship the God above. The way of conversion for kings is the same as for ourselves: faith to them also cometh by hearing, and hearing by the word of God. Happy are those who can cause the word of the Lord to penetrate palaces; for the occupants of thrones are usually the last to know the joyful sounds of the gospel. David, the king, cared for kings' souls, and it will be wise for each man to look first after those who are of his own order. He went to his work of testimony with full assurance of success: he meant to speak only the words of Jehovah's mouth, and he felt sure that the kings would hear and praise Jehovah.

Psalm 138:5

"Yea, they shall sing in the ways of the Lord." Here is a double wonder - kings in God's ways, and kings singing there. Let a man once know the ways of Jehovah, and he will find therein abundant reason for song; but the difficulty is to bring the great ones of the earth into ways so little attractive to the carnal mind. Perhaps when the Lord sends us a King David to preach, we shall yet see monarchs converted and hear their voices raised in devout adoration. "For great is the glory of the Lord." This glory shall overshadow all the greatness and glory of all kings: they shall be stirred by a sight of it to obey and adore. O that Jehovah's glory were revealed even now! O that the blind eyes of men could once behold it, then their hearts would be subdued to joyful reverence. David, under a sense of Jehovah's glory, exclaimed, "I will sing" (Psalm 138:1), and here he represents the kings as doing the same thing.

Either,

1. All neighbouring kings; or,

2. The generality of kings and princes upon earth. And so this is a prophecy of the calling of the Gentiles, which seems to be confirmed by the next verse, which expresseth their extraordinary joy; and an eminent advancement of God’s glory, which agrees much better to this great occasion, than to that of David’s exaltation to the throne, wherein the other kings of the earth were not much concerned.

The words of thy mouth; either,

1. Thy promises declared unto them by me; or,

2. The gospel preached among them.

All the kings of the earth shall praise thee, O Lord,.... Or "let them confess", or "praise thee" (s); a wish or prayer. Not only the kings known to David, as Kimchi limits it; or that lived in his days, as Hiram and others; but in the latter day, when they shall come to Zion, the church, and be nursing fathers to it, and shall serve and worship the King Messiah, Isaiah 49:23;

when they hear the words of thy mouth; either the promises of it fulfilled not only with respect to David; but the Messiah, and his church and people, in the latter day, even the glorious things spoken thereof: or the doctrines of the Gospel, which are the words of his mouth, and more desirable than thousands of gold and silver; and which, when kings shall hear so as to understand, they will praise the Lord for them; see Isaiah 52:15. The Targum is,

"the words of thy praise.''

(s) "confiteantur tibi", V. L. Pagninus, Montanus.

All the {d} kings of the earth shall praise thee, O LORD, when they hear the words of thy mouth.

(d) All the world will confess that you have wonderfully preserved me, and performed your promise.