Charles Ellicott Commentary Psalms 138:4-5

"All the kings of the earth shall give thee thanks, O Jehovah, For they have heard the words of thy mouth. Yea, they shall sing of the ways of Jehovah; For great is the glory of Jehovah." — Psalms 138:4-5 (ASV)

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.”