*Minor differences ignored. Grouped by changes, with first version listed as example.
Because this psalm is composed of parts taken from the fifty-seventh and sixtieth psalms, it would be superfluous to repeat, in this place, what we have already said by way of exposition in those psalms. [1]
1 - "The 108th psalm is altogether made up of extracts from the others; its first part being identical (with the exceptions of a few slight variations) with the third division of the 57th; its second, with the second division of the 60th. And both these borrowed parts are discriminated, both in the 57th and 60th psalms, from the rest of the context by the word Selah. This is a remarkable fact, and illustrates strongly one of the functions of the Diapsalma. These parts were, then, to a certain degree, regarded as distinct compositions, which occasionally were disjointed from their original context; the very change of sentiment and strain, which originated the word Diapsalma, sanctioning such an occasional practice." -- Jebb's Literal Version of the Book of Psalms, with Dissertations, volume 2, page 109.
O God, my heart is fixed - Prepared, suited, ready. See the notes at Psalm 57:7. In Psalm 57:7, this is repeated: "My heart is fixed; O God, my heart is fixed:" indicating that there "might" have been some doubt or vacillation caused by the circumstances then existing, and the repetition would have respect to that, as if the psalmist had been unsettled and wavering for a time, but was at last firm. In such circumstances it would not be unnatural to "repeat" the assertion, as if there were no longer any doubt. In the beginning of a psalm, however, where there had been no previous expression or feeling of doubt so far as appears, there would be no propriety in repeating the assertion.
I will sing and give praise - See the notes at Psalm 57:7.
Even with my glory - This is not in Psalm 57:1-11. It is literally here, "truly my glory." In Psalm 57:8, however, the expression, "Awake up, my glory," occurs, and this seems to correspond with that language. It means here that it was his glory - his honor - thus to be employed in giving praise to God. It was worthy of all that there was elevated in his nature; of all that constituted his glory; of his highest powers. At no time is man employed in a more noble and lofty work than praise.
Even with my glory - My greatest glory shall be in publishing thy praise. Some make the glory here to mean the Lord himself; some, the Ark of the covenant; some, the Soul of the psalmist; others, his Tongue; some, the Gift of Prophecy; and some, the psalmist's Spirit or Vein of poetry. See the notes on Psalm 57:8.
"A Song [or] Psalm of David." O God, my heart is (a) fixed; I will sing and give praise, even with my glory.
(a) This earnest affection declares that he is free from hypocrisy and that sluggishness does not stop him.
O God, my heart is fixed; I will sing and give praise,.... From hence to Psalm 108:6 the words are taken out of Psalm 57:7, which see.
Even with my glory; my tongue; in Psalm 57:8, it is read, "awake up my glory". See Gill on Psalm 57:7,
We may usefully select passages from different psalms, as here, Psalm 57:1-11 and Psalm 60:1-12, to help our devotions, and enliven our gratitude. When the heart is firm in faith and love, the tongue, being employed in grateful praises, is our glory. Every gift of the Lord honours and profits the possessor, as it is employed in God's service and to his glory. Believers may pray with assured faith and hope, for all the blessings of salvation; which are secured to them by the faithful promise and covenant of God. Then let them expect from him help in every trouble, and victory in every conflict. Whatever we do, whatever we gain, God must have all the glory. Lord, visit all our souls with this salvation, with this favour which thou bearest to thy chosen people.
This first half is taken from Ps. 57:8-12. The repetition of confident is my heart in Psalm 57:1-11 is here omitted; and in place of it the "my glory" of the exclamation, awake my glory, is taken up to "I will sing and will harp" as a more minute definition of the subject (vid., on Psalm 3:5): He will do it, yea,his soul with all its godlike powers shall do it. Jahve in Psalm 108:4 is transformed out of the Adonaj; and Waw copul. is inserted both before Psalm 108:4 and Psalm 108:6, contrary to Psalm 57:1-11. מעל, Psalm 108:5 (as in Esther 3:1), would be a pleasing change for עד if Psalm 108:5 followed Psalm 108:5 and the definition of magnitude did not retrograde instead of heightening. Moreover Psalm 36:6; Jeremiah 51:9 (cf. על in Psalm 113:4; Psalm 148:13) favour עד in opposition to מעל.
Glory - With my tongue.
*More commentary available at chapter level.