A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 103:1A Psalm of joyous praise, in which the writer rises from a thankful acknowledgment of personal blessings to a lively celebration of God's gracious attributes, as not only intrinsically worthy of praise, but as specially suited to man's frailty. He concludes by invoking all creatures to unite in his song. (Psa. 103:1-22)
Bless, &c.--when God is the object, praise.
my soul--myself (Psa 3:3; Psa 25:1), with allusion to the act, as one of intelligence.
all . . . within me-- (Deu 6:5).
his holy name-- (Psa 5:11), His complete moral perfections.
psa 103:2forget not all--not any, none of His benefits.
psa 103:3diseases--as penal inflictions (Deu 29:22; Ch2 21:19).
psa 103:4redeemeth--Cost is implied.
destruction--literally, "pit of corruption" (Psa 16:10).
crowneth--or, "adorneth" (Psa 65:11).
tender mercies--compassions (compare Psa 25:6; Psa 40:11).
psa 103:5By God's provision, the saint retains a youthful vigor like the eagles (Psa 92:14; compare Isa 40:31).
psa 103:6Literally, "righteousness and judgments," denoting various acts of God's government.
psa 103:7ways--of providence, &c., as usual (Psa 25:4; Psa 67:2).
acts--literally, "wonders" (Psa 7:11; Psa 78:17).
psa 103:8God's benevolence implies no merit. He shows it to sinners, who also are chastened for a time (Exo 34:6).
keep (anger)--in Lev 19:18, bear a grudge (Jer 3:5, Jer 3:12).
psa 103:12removed . . . from us--so as no longer to affect our relations to Him.
psa 103:13pitieth--literally, "has compassion on."
psa 103:14he--"who formed," Psa 94:9.
knoweth our frame--literally, "our form."
we are dust--made of and tending to it (Gen 2:7).
psa 103:15So short and frail is life that a breath may destroy it.
it is gone--literally, "it is not."
know it no more--no more recognize him (Psa 90:6; Isa 40:6-8).
psa 103:17For similar contrast compare Psa 90:2-6; Psa 102:27-28.
psa 103:18such . . . covenant--limits the general terms preceding.
righteousness--as usual (Psa 7:17; Psa 31:1).
psa 103:19God's firm and universal dominion is a pledge that He will keep His promises (Psa 11:4; Psa 47:8).
psa 103:20do his commandments . . . word--or, literally, "so as to hearken," &c., that is, their acts of obedience are prompt, so that they are ever ready to hear, and know, and follow implicitly His declared will (compare Deu 26:17; Luk 1:19).
psa 103:21ye his hosts--myriads, or armies, as corresponding to angels of great power [Psa 103:20], denoting multitudes also.
psa 103:22all his works--creatures of every sort, everywhere.