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 37:1A composed and uniform trust in God and a constant course of integrity are urged in view of the blessedness of the truly pious, contrasted in various aspects with the final ruin of the wicked. Thus the wisdom and justice of God's providence are vindicated, and its seeming inequalities, which excite the cavils of the wicked and the distrust of the pious, are explained. David's personal history abundantly illustrates the Psalm. (Psa. 37:1-40)
The general sentiment of the whole Psalm is expressed. The righteous need not be vexed by the prosperity of the wicked; for it is transient, and their destiny undesirable.
psa 37:3Trust--sure of safety.
shalt thou dwell--or, "dwell thou"; repose quietly.
verily . . . fed--or, "feed on truth," God's promise (Psa 36:5; compare Hos 12:1).
psa 37:4desires-- (Psa 20:5; Psa 21:2), what is lawful and right, really good (Psa 84:11).
psa 37:5Commit thy way-- (Pro 16:3). Works--what you have to do and cannot set forth as a burden.
trust . . . in him--literally, "on Him." He will do what you cannot (compare Psa 22:8; Psa 31:6). He will not suffer your character to remain under suspicion.
psa 37:7Rest in--literally, "Be silent to the Lord."
and wait--Be submissive--avoid petulance and murmurings, anger and rash doing.
psa 37:9Two reasons: The prosperity of the wicked is short; and the pious, by humble trust, will secure all covenant blessing, denoted here by "inherit the earth" (compare Psa 25:13).
psa 37:10shall not be--literally, "is not"--is not to be found.
psa 37:11peace--includes prosperity.
psa 37:12gnasheth . . . teeth--in beastly rage.
psa 37:13(Compare Psa 2:4).
his day--of punishment, long delayed, shall yet come (Heb 10:37).
psa 37:14sword, and . . . bow--for any instruments of violence.
slay--literally, "slaughter" (Sa1 25:11).
poor and needy--God's people (Psa 10:17; Psa 12:5). The punishment of the wicked as drawn on themselves--often mentioned (compare Psa 7:15-16; Psa 35:8).
psa 37:16riches--literally, "noise and tumult," as incidental to much wealth (compare Psa 39:6). Thus the contrast with the "little" of one man is more vivid.
psa 37:17Even the members of the body needed to hold weapons are destroyed.
psa 37:18God, who knows His people's changes, provides against evil and supplies all their need.
psa 37:20While the wicked, however mighty, are destroyed, and that utterly, as smoke which vanishes and leaves no trace.
psa 37:21payeth not--not able; having grown poor (compare Deu 15:7). Ability of the one and inability of the other do not exclude moral dispositions. God's blessing or cursing makes the difference.
psa 37:22cut off--opposed to "inherit the earth" (compare Lev 7:20-21).
psa 37:23steps--way, or, "course of life"; as ordered by God, failures will not be permanent.
psa 37:26his seed is blessed--literally, "for a blessing" (Gen 12:2; Psa 21:6). This position is still true as the rule of God's economy (Ti1 4:8; Ti1 6:6).
psa 37:27The exhortation is sustained by the assurance of God's essential rectitude in that providential government which provides perpetual blessings for the good, and perpetual misery for the wicked.
psa 37:30The righteous described as to the elements of character, thought, word, and action.
psa 37:31steps--or, "goings"--for conduct which is unwavering (Psa 18:36).
psa 37:32The devices of the wicked against the good fail because God acquits them.
psa 37:34On the contrary, the good are not only blessed, but made to see the ruin of their foes.
psa 37:35of which a picture is given, under the figure of a flourishing tree (compare Margin), which soon withers.
psa 37:36he was not--(Compare Psa 37:10).
psa 37:37By "the end" is meant reward (Pro 23:18; Pro 24:14), or expectation of success, as in Psa 37:38, which describes the end of the wicked in contrast, and that is cut off (compare Psa 73:17).
psa 37:38together--at once; entirely (Psa 4:8).
psa 37:39strength-- (Psa 27:1; Psa 28:8).
trouble--straits (Psa 9:9; Psa 10:1). In trust and quietness is the salvation of the pious from all foes and all their devices.