Verse 1-2
Psalms 138:1-2. I will praise thee with my whole heart — With uprightness of intention, and fervency of affection. Before the gods will I sing praises, &c. — Before kings and princes, or, before judges and great men, either those of other nations who visited him, or those of his own nation that attended on him. He will not only praise God in his heart, which he might do, by pious ejaculations, in any company, but will sing praise with his voice, if there should be occasion. I will worship toward thy holy temple — Where the ark was. He saith, toward it, because he was not permitted to enter into it. For thy loving-kindness and for thy truth — For thy goodness and for thy promises; 1st, For promising me singular blessings out of thy mere grace and favour; and, 2d, For performing thy promises most faithfully. For thou hast magnified thy word, &c. — Thou hast glorified thy faithfulness, in fulfilling thy promises unto me, more than any other of thy glorious perfections by which thou art known. Not that one of God’s attributes is really, and in itself, more great or glorious than another; or can be made so, but because one may be more celebrated and admired by men than another; as here, God’s gracious promise of the kingdom made to David, and the wonderful accomplishment thereof, in spite of all those difficulties which stood in the way, and which seemed to men to be insuperable, was, at this time, more observed and admired than any other of his attributes or actions.

Verse 3
Psalms 138:3. In the day when I cried thou answeredst me — Didst give me to understand that my prayer was accepted, and should have a gracious return in due time; and strengthenedst me, in my soul — This clause limits and explains the former, and shows in what way God answered him so speedily, namely, not by giving him the very thing which he desired in that very instant, but by giving him inward support and patience, to wait God’s time, and to bear all his troubles cheerfully in the mean time, which was a singular mercy, and, indeed, greater than the actual donation of any temporal blessing. Observe, reader, if God give us strength in our souls, to bear the burdens, resist the temptations, and to do the duties, of an afflicted state; if he strengthen us to rely on him by faith, to maintain the peace of our own minds, and to wait with patience for the issue, we must own that he hath answered us, and are bound to be thankful.

Verse 4-5
Psalms 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, Psalms 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.

Verse 6
Psalms 138:6. Though the Lord be high — And neither need any of his creatures, nor can be benefited by them. Yet hath he respect unto the lowly — Unto such as are mean and obscure in the world; to me, a poor contemptible shepherd, whom he hath preferred before great princes; and to such as are little in their own eyes. But the proud he knoweth afar off — But, as for the great men of the world, who are lifted up in pride, he looks upon them, as they do upon others, with scorn and contempt, and keeps them at a great distance, as disdaining to admit them into his presence.

Verse 7-8
Psalms 138:7-8. Though I walk in the midst of trouble — That is, be compassed with dangers; thou wilt revive me — Thou wilt cheer my spirit and preserve my life. Thou shalt stretch forth thy hand — Put forth thy almighty power; against the wrath of mine enemies — To oppose and restrain their rage. The Lord will perfect that which concerneth me — Will finish that great work of my deliverance and advancement, which he hath undertaken, and carried on hitherto. Thy mercy endureth for ever — It is not inconstant and changeable, as men’s affections are, but everlasting. And this may be either produced as a proof of the foregoing assertion, The Lord will perfect, &c. — Or, as an argument to enforce the following petition. Forsake not — Do not withdraw thy presence from me, who am thy creature, but continue to support and save me. Or, leave not, or, do not desist from, or, cease to carry on, as תרŠ, rather signifies, the work, namely of my salvation, which is thus far advanced, not by any human help, but by thy power and providence.