Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
This little song is inscribed לדוד because it is like an echo of the answer (Sa2 6:21.) with which David repelled the mocking observation of Michal when he danced before the Ark in a linen ephod, and therefore not in kingly attire, but in the common raiment of the priests: I esteem myself still less than I now show it, and I appear base in mine own eyes. In general David is the model of the state of mind which the poet expresses here. He did not push himself forward, but suffered himself to be drawn forth out of seclusion. He did not take possession of the throne violently, but after Samuel has anointed him he willingly and patiently traverses the long, thorny, circuitous way of deep abasement, until he receives from God's hand that which God's promise had assured to him. The persecution by Saul lasted about ten years, and his kingship in Hebron, at first only incipient, seven years and a half. He left it entirely to God to remove Saul and Ishbosheth. He let Shimei curse. He left Jerusalem before Absalom. Submission to God's guidance, resignation to His dispensations, contentment with that which was allotted to him, are the distinguishing traits of his noble character, which the poet of this Psalm indirectly holds up to himself and to his contemporaries as a mirror, viz., to the Israel of the period after the Exile, which, in connection with small beginnings under difficult circumstances, had been taught humbly contented and calm waiting.
With לבּי לא־גבהּ the poet repudiates pride as being the state of his soul; with לא־רמוּ עיני (lo-ramū' as in Pro 30:13, and before Ajin, e.g., also in Gen 26:10; Isa 11:2, in accordance with which the erroneous placing of the accent in Baer's text is to be corrected), pride of countenance and bearing; and with ולא־הלּכתּי, pride of endeavour and mode of action. Pride has its seat in the heart, in the eyes especially it finds its expression, and great things are its sphere in which it diligently exercises itself. The opposite of "great things" (Jer 23:3; Jer 45:5) is not that which is little, mean, but that which is small; and the opposite of "things too wonderful for me" (Gen 18:14) is not that which is trivial, but that which is attainable.
אם־לא does not open a conditional protasis, for where is the indication of the apodosis to be found? Nor does it signify "but," a meaning it also has not in Gen 24:38; Eze 3:6. In these passages too, as in the passage before us, it is asseverating, being derived from the usual formula of an oath: verily I have, etc. שׁוּה signifies (Isa 28:25) to level the surface of a field by ploughing it up, and has an ethical sense here, like ישׂר with its opposites עקב and עפּל. The Poel סּומם is to be understood according to דּוּמיּה in Psa 62:2, and דּוּמם in Lam 3:26. He has levelled or made smooth his soul, so that humility is its entire and uniform state; he has calmed it so that it is silent and at rest, and lets God speak and work in it and for it: it is like an even surface, and like the calm surface of a lake. Ewald and Hupfeld's rendering: "as a weaned child on its mother, so my soul, being weaned, lies on me," is refuted by the consideration that it ought at least to be כּגמוּלה, but more correctly כּן גמולה; but it is also besides opposed by the article which is swallowed up in כּגּמל, according to which it is to be rendered: like one weaned beside its mother (here כּגמול on account of the determinative collateral definition), like the weaned one (here כּגּמול because without any collateral definition: cf. with Hitzig, Deu 32:2, and the like; moreover, also, because referring back to the first גמול, cf. Hab 3:8), is my soul beside me (Hitzig, Hengstenberg, and most expositors). As a weaned child - viz. not one that is only just begun to be weaned, but an actually weaned child (גּמל, cognate גּמר eta, to bring to an end, more particularly to bring suckling to an end, to wean) - lies upon its mother without crying impatiently and craving for its mother's breast, but contented with the fact that it has its mother - like such a weaned child is his soul upon him, i.e., in relation to his Ego (which is conceived of in עלי as having the soul upon itself, cf. Psa 42:7; Jer 8:18; Psychology, S. 151f., tr. p. 180): his soul, which is by nature restless and craving, is stilled; it does not long after earthly enjoyment and earthly good that God should give these to it, but it is satisfied in the fellowship of God, it finds full satisfaction in Him, it is satisfied (satiated) in Him.
By the closing strain, Psa 131:3, the individual language of the Psalm comes to have a reference to the congregation at large. Israel is to renounce all self-boasting and all self-activity, and to wait in lowliness and quietness upon its God from now and for evermore. For He resisteth the proud, but giveth grace unto the humble.