Jamieson, Fausset and Brown on Psalms 104:35

35. Those 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.