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 104:1The Psalmist celebrates God's glory in His works of creation and providence, teaching the dependence of all living creatures; and contrasting the happiness of those who praise Him with the awful end of the wicked. (Psa. 104:1-35)
God's essential glory, and also that displayed by His mighty works, afford ground for praise.
psa 104:2light--is a figurative representation of the glory of the invisible God (Mat 17:2; Ti1 6:16). Its use in this connection may refer to the first work of creation (Gen 1:3).
stretchest out the heavens--the visible heavens or sky which cover the earth as a curtain (Isa 40:12).
psa 104:3in the waters--or, it may be "with"; using this fluid for the beams, or frames, of His residence accords with the figure of clouds for chariots, and wind as a means of conveyance.
walketh--or, "moveth" (compare Psa 18:10-11; Amo 9:6).
psa 104:4This is quoted by Paul (Heb 1:7) to denote the subordinate position of angels; that is, they are only messengers as other and material agencies.
flaming fire-- (Psa 105:32) being here so called.
psa 104:5The earth is firmly fixed by His power.
psa 104:6These verses rather describe the wonders of the flood than the creation (Gen 7:19-20; Pe2 3:5-6). God's method of arresting the flood and making its waters subside is poetically called a "rebuke" (Psa 76:6; Isa 50:2), and the process of the flood's subsiding by undulations among the hills and valleys is vividly described.
psa 104:10Once destructive, these waters are subjected to the service of God's creatures. In rain and dew from His chambers (compare Psa 104:3), and fountains and streams, they give drink to thirsting animals and fertilize the soil. Trees thus nourished supply homes to singing birds, and the earth teems with the productions of God's wise agencies,
psa 104:14so that men and beasts are abundantly provided with food.
for the service--literally, "for the culture," &c., by which he secures the results.
oil . . . shine--literally, "makes his face to shine more than oil," that is, so cheers and invigorates him, that outwardly he appears better than if anointed.
strengtheneth . . . heart--gives vigor to man (compare Jdg 19:5).
psa 104:16God's care of even wild animals and uncultivated parts of the earth.
psa 104:20He provides and adapts to man's wants the appointed times and seasons.
psa 104:24From a view of the earth thus full of God's blessings, the writer passes to the sea, which, in its immensity, and as a scene and means of man's activity in commerce, and the home of countless multitudes of creatures, also displays divine power and beneficence. The mention of
psa 104:26leviathan-- (Job 40:20) heightens the estimate of the sea's greatness, and of His power who gives such a place for sport to one of His creatures.
psa 104:27The entire dependence of this immense family on God is set forth. With Him, to kill or make alive is equally easy. To hide His face is to withdraw favor (Psa 13:1). By His spirit, or breath, or mere word, He gives life. It is His constant providence which repairs the wastes of time and disease.
psa 104:31While God could equally glorify His power in destruction, that He does it in preservation is of His rich goodness and mercy, so that we may well spend our lives in grateful praise, honoring to Him, and delightful to pious hearts (Psa 147:1).
psa 104:35Those who refuse such a protector and withhold such a service mar the beauty of His works, and must perish from His presence.
Praise ye the Lord--The Psalm closes with an invocation of praise, the translation of a Hebrew phrase, which is used as an English word, "Hallelujah," and may have served the purpose of a chorus, as often in our psalmody, or to give fuller expression to the writer's emotions. It is peculiar to Psalms composed after the captivity, as "Selah" is to those of an earlier date.