Jamieson, Fausset & Brown

The voice--the same divine herald as in Isa 40:3. he--one of those ministers or prophets (see on Isa 40:1) whose duty it was, by direction of "the voice," to "comfort the Lord's afflicted people with the promises of brighter days." All flesh is grass--The connection is, "All human things, however goodly, are transitory: God's promises alone steadfast" (Isa 40:8, Isa 40:15, Isa 40:17, Isa 40:23-24); this contrast was already suggested in Isa 40:5, "All flesh . . . the mouth of the Lord." Pe1 1:24-25 applies this passage distinctly to the gospel word of Messiah (compare Joh 12:24; Jam 1:10).