Charles Ellicott Commentary Isaiah 26:3

"Thou wilt keep [him] in perfect peace, [whose] mind [is] stayed [on thee]; because he trusteth in thee." — Isaiah 26:3 (ASV)

Thou wilt keep him in perfect peace. —The italics show that the English version is supplemented with several interpolated words. More literally, and more impressively, we read, You establish a firm purpose; peace, peace, for in You is his trust. Completeness is expressed, as elsewhere, in the form of iteration. No adjectives can add to the fullness of the meaning of the noun.