Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
The Mediator and Perfecter
There will come a time when the praise of Jahve, which according to Psa 137:3 was obliged to be dumb in the presence of the heathen, will, according to Psa 138:5, be sung by the kings of the heathen themselves. In the lxx Psa 137:1-9 side by side with τῷ Δαυίδ also has the inscription Ἱιερεμίου, and Psa 138:1-8 has Ἀγγαίου καὶ Ζαχαρίου. Perhaps these statements are meant to refer back the existing recension of the text of the respective Psalms to the prophets named (vid., Khler, Haggai, S. 33). From the fact that these names of psalmodists added by the lxx do not come down beyond Malachi, it follows that the Psalm-collection in the mind of the lxx was made not later than in the time of Nehemiah.
The speaker in Psa 138:1-8, to follow the lofty expectation expressed in Psa 138:4, is himself a king, and according to the inscription, David. There is, however, nothing to favour his being the author; the Psalm is, in respect for the Davidic Psalms, composed as it were out of the soul of David - an echo of 2 Sam. 7 (1 Chr. 17). The superabundant promise which made the throne of David and of his seed an eternal throne is here gratefully glorified. The Psalm can at any rate be understood, if with Hengstenberg we suppose that it expresses the lofty self-consciousness to which David was raised after victorious battles, when he humbly ascribed the glory to God and resolved to build Him a Temple in place of the tent upon Zion.
The poet will give thanks to Him, whom he means without mentioning Him by name, for His mercy, i.e., His anticipating, condescending love, and for His truth, i.e., truthfulness and faithfulness, and more definitely for having magnified His promise (אמרה) above all His Name, i.e., that He has given a promise which infinitely surpasses everything by which He has hitherto established a name and memorial for Himself (על־כּל־שׁמך, with ō instead of ŏ, an anomaly that is noted by the Masora, vid., Baer's Psalterium, p. 133). If the promise by the mouth of Nathan (2 Sam. 7) is meant, then we may compare Sa2 7:21. גּדל, גּדול, גּדלּה are repeated in that promise and its echo coming from the heart of David so frequently, that this הגדּלתּ seems like a hint pointing to that history, which is one of the most important crises in the history of salvation. The expression נגד אלהים also becomes intelligible from this history. Ewald renders it: "in the presence of God!" which is surely meant to say: in the holy place (De Wette, Olshausen). But "before God will I sing praise to Thee (O God!)" - what a jumble! The lxx renders ἐναντίον ἀγγέλων, which is in itself admissible and full of meaning,
(Note: Bellarmine: Scio me psallentem tibi ab angelis, qui tibi assistunt, videri et attendi et ideo ita considerate me geram in psallendo, ut qui intelligam, in quo theatro consistam.)
but without coherence in the context of the Psalm, and also is to be rejected because it is on the whole very questionable whether the Old Testament language uses אלהים thus, without anything further to define it, in the sense of "angels." It might be more readily rendered "in the presence of the gods," viz., of the gods of the peoples (Hengstenberg, Hupfeld, and Hitzig); but in order to be understood of gods which are only seemingly such, it would require some addition. Whereas אלהים can without any addition denote the magisterial possessors of the dignity that is the type of the divine, as follows from Psa 82:1 (cf. Psa 45:7) in spite of Knobel, Graf, and Hupfeld; and thus, too (cf. נגד מלכים in Psa 119:46), we understand it here, with Rashi, Aben-Ezra, Kimchi, Falminius, Bucer, Clericus, and others. What is meant are "the great who are in the earth," Sa2 7:9, with whom David, inasmuch as he became king from being a shepherd, is ranked, and above whom he has been lifted up by the promise of an eternal kingship. Before these earthly "gods" will David praise the God of the promise; they shall hear for their salutary confusion, for their willing rendering of homage, that God hath made him "the highest with respect to the kings of the earth" (Psa 89:28).
There are two things for which the poet gives thanks to God: He has answered him in the days of trouble connected with his persecution by Saul and in all distresses; and by raising him to the throne, and granting him victory upon victory, and promising him the everlasting possession of the throne, He has filled him with a proud courage, so that lofty feeling has taken up its abode in his soul, which was formerly fearful about help. Just as רהב signifies impetuosity, vehemence, and then also a monster, so הרהיב signifies both to break in upon one violently and overpowerlingly (Sol 6:5; cf. Syriac arheb, Arabic arhaba, to terrify), and to make any one courageous, bold, and confident of victory. בּנפשׁי עז forms a corollary to the verb that is marked by Mugrash or Dech: so that in my soul there was עז, i.e., power, viz., a consciousness of power (cf. Jdg 5:21). The thanksgiving, which he, the king of the promise, offers to God on account of this, will be transmitted to all the kings of the earth when they shall hear (שׁמעוּ in the sense of a fut. exactum) the words of His mouth, i.e., the divine אמרה, and they shall sing of (שׁיר with בּ, like דּבּר בּ in Psa 87:3, שׂיח בּ in Psa 105:2 and frequently, הלּל בּ in Psa 44:9, הזכּיר בּ in Psa 20:8, and the like) the ways of the God of the history of salvation, they shall sing that great is the glory of Jahve. Psa 138:6 tells us by what means He has so super-gloriously manifested Himself in His leadings of David. He has shown Himself to be the Exalted One who is His all-embracing rule does not leave the lowly (cf. David's confessions in Psa 131:1; Sa2 6:22) unnoticed (Psa 113:6), but on the contrary makes him the especial object of His regard; and on the other hand even from afar (cf. Psa 139:2) He sees through (ידע as in Psa 94:11; Jer 29:23) the lofty one who thinks himself unobserved and conducts himself as if he were answerable to no higher being (Psa 10:4). In correct texts וגבה has Mugrash, and ממרחק Mercha. The form of the fut. Kal יידע is formed after the analogy of the Hiphil forms ייליל in Isa 16:7, and frequently, and ייטיב in Job 24:21; probably the word is intended to be all the more emphatic, inasmuch as the first radical, which disappears in ידע, is thus in a certain measure restored.
(Note: The Greek imperfects with the double (syllabic and temporal) augment, as ἑώρων, ἀνέῳγον, are similar. Chajuǵ also regards the first Jod in these forms as the preformative and the second as the radical, whereas Abulwald, Gramm. ch. xxvi. p. 170, explains the first as a prosthesis and the second as the preformative. According to the view of others, e.g., of Kimchi, יידע might be fut. Hiph. weakened from יהדע (יהידיע), which, apart from the unsuitable meaning, assumes a change of consonants that is all the more inadmissible as ידע itself springs from ודע. Nor is it to be supposed that יידע is modified from יידע (Luzzatto, 197), because it is nowhere written יידע.)
Out of these experiences-so important for all mankind - of David, who has been exalted by passing through humiliation, there arise from him confident hopes concerning the future. The beginning of this strophe calls Psa 23:4 to mind. Though his way may lead through the midst of heart - oppressing trouble, Jahve will loose these bands of death and quicken him afresh (חיּה as in Psa 30:4; Psa 71:20, and frequently). Though his enemies may rage, Jahve will stretch forth His hand threateningly and tranquillizingly over their wrath, and His right hand will save him. ימינך is the subject according to Psa 139:10 and other passages, and not (for why should it be supposed to be this?) accus. instrumenti (vid., Psa 60:7). In Psa 138:8 יגמר is intended just as in Psa 57:3 : the word begun He will carry out, ἐπιτελεῖν (Phi 1:6); and בּעדי (according to its meaning, properly: covering me) is the same as עלי in that passage (cf. Psa 13:6; 142:8). The pledge of this completion is Jahve's everlasting mercy, which will not rest until the promise is become perfect truth and reality. Thus, therefore, He will not leave, forsake the works of His hands (vid., Psa 90:16.), i.e., as Hengstenberg correctly explains, everything that He has hitherto accomplished for David, from his deliverance out of the hands of Saul down to the bestowment of the promise - He will not let one of His works stand still, and least of all one that has been so gloriously begun. הרפּה (whence תּרף) signifies to slacken, to leave slack, i.e., leave uncarried out, to leave to itself, as in Neh 6:3. אל expresses a negation with a measure of inward excitement.