Charles H. Spurgeon on Psalms 138:1

Psalm 138:1 to 145:21. These eight Psalms are composed in the first person, and they follow very happily after the fifteen "Songs of Up goings", and the three Psalms of praise uttered by the chorus of those who have gone up to Sion. Those Psalms were the united utterances of national devotion. These eight Psalms are the devout Israelite's Manual of private prayer and praise. —Christopher Wordsworth.

Whole Psalm. This is the first of a series of eight Psalms (Ps 138:1-145:21), probably the last composed by David, a kind of commentary on the great Messianic promise in 2Sa 7:1-29. They are found in this part of the psalter, in consequence of having been made the basis, or rather the body, of a system or series (Ps 135:1-146:10) by a later writer. —Joseph Addison Alexander.

Whole Psalm. If this Psalm refers to the promise in 2Sa 7:1-29, there can be no doubt of the correctness of the superscription, which ascribes it to David. For he, on whom the promise has been conferred, himself stands forth as the speaker. Proof also of David's authorship is found in the union, so characteristic of him, of bold courage, see especially Ps 138:3, and deep humility, see Ps 138:6. And in proof of the same comes, finally, the near relationship in which it stands with the other Psalms of David, especially those which likewise refer to the promise of the everlasting kingdom; and with David's thanksgiving in 2Sa 7:1-29, the conclusion of which remarkably agrees with the conclusion of our Psalm: "And now, Lord God, the word which thou hast spoken upon thy servant and upon his house, that fulfil even to eternity, and do as thou hast spoken." —E.W. Hengstenberg.

I will praise thee with my whole heart. It is a part of our thankfulness to engage our heart to praise God in time to come, since we find that all the thanks we can give for the present are short of our duty or desire to praise him: "I will praise thee", saith David. Sometimes the believer will find his heart set at liberty in God's worship, which at another time he will find to be in bands, and then he should take the opportunity of an enlarged heart to run in the way of God's service, as David doth here: "I will praise thee with my whole heart." —David Dickson.