Quotation from Isa 40:6-8 (partly like the lxx, partly like the Hebrew).
For (dioti). As in 1Pe 1:16 (dia and hoti), “for that.” So in 1Pe 2:6. See a free use of this imagery about the life of man as grass and a flower in Jam 1:11. The best MSS. here read autēs (thereof) after doxa (glory) rather than anthrōpou (of man).
Withereth (exēranthē). First aorist (gnomic, timeless) passive indicative of xērainō (see Jam 1:11).
Falleth (exepesen). Second aorist (gnomic, timeless) active indicative of ekpiptō (see Jam 1:11).