fir tree - the godly (Isa 60:13; Psa 92:12). Compare as to the change wrought, Rom 6:19.
brier - emblem of uncultivation (Isa 5:6).
myrtle - Hebrew, Hedes, from which comes Hedassah, the original name of Esther. Type of the Christian Church; for it is a lowly, though beautiful, fragrant, and evergreen shrub (Psa 92:13, Psa 92:14).
for a name ... everlasting sign - a perpetual memorial to the glory of Jehovah (Jer 13:11; Jer 33:9).