4. as a brier—or thorn; pricking with injury all who come in contact with them (2Sa 23:6, 7; Isa 55:13; Eze 2:6).
the day of thy watchmen—the day foretold by thy (true) prophets, as the time of "thy visitation" in wrath [Grotius]. Or, "the day of thy false prophets being punished"; they are specially threatened as being not only blind themselves, but leading others blindfold [Calvin].
now—at the time foretold, "at that time"; the prophet transporting himself into it.
perplexity—(Isa 22:5). They shall not know whither to turn.