Who can remain silent when he has been made partaker of so great a salvation?
"A Psalm of David". - Doubtless by David; it is in his own style when at its best, and we should attribute it to his later years when he had a higher sense of the preciousness of pardon, because a keener sense of sin, than in his younger days. His clear sense of the frailty of life indicates his older, weaker years, as also does the very fulness of his praiseful gratitude. We cannot be half married; neither can we love the LORD our God with only part of our heart, part of our soul, and part of our strength (Deuteronomy 6:5). So cannot David, so cannot the remnant, and so cannot we, in Psalm 103 praise God with only a part of what is in him, in them, or in us.
All of God's actions flow from Who He is and bear His inscription. Who He is and what He does calls for praise by David's whole person. Psalms 103:1 is blessing, or praising, the LORD for Who He is; Psalms 103:2 for what He does. The latter continues until Psalms 103:18. Then in 103:19, Who He is becomes as the occasion for praising and giving thanks to Him in Psalms 103:20-22.
The Psalmist begins by calling upon his own soul to declare its gratitude for the manifestations of God’s favor, which he has himself personally experienced (103:1-5), and the words which are uttered at the beginning of the Psalm reappear in the last line, and thus enclose the whole. Between these, the Psalmist celebrates God’s gracious and helpful dealings in their actual manifestations in Israel (103:6-10), in their heavenly exaltation and paternal character, and their relation to sinful and mortal men (103:11~14), and in their trustworthiness for all who hold fast to His covenant and to His ordinances (103:15~18). Then the whole world is called upon to praise this heavenly King who rules over all (103:19~22).