INTRODUCTION TO PSALM 138 A Psalm of David. This psalm is generally thought to have been written by David upon his being advanced to the throne; on account of which he praises the Lord, who had supported him under many exercises, and had made good his promise to him, at least in part; and he firmly believed the accomplishment of the rest, that he would perfect what concerned him, Psa 138:8. It seems as if this psalm was composed between his being king over Judah and over all Israel. Though Theodoret understands the psalm as a thanksgiving of the Jews upon their return from Babylon, which David prophesied of. The Syriac version calls it a thanksgiving with a prophecy; as indeed it is a prophecy of the Messiah's kingdom, and of the calling of the Gentiles in the latter day, as appears from Psa 138:4.