{Shall not be hurt} (ou m(8820)adik(8874)h(8869)). Strong double
negative with first aorist passive subjunctive of adike(935c), old
verb, to act unjustly (from adikos), here to do harm or wrong
to one, old usage as in  6:6  7:2f.  9:4,10  11:5 . {Of the
second death} (ek tou thanatou tou deuterou). Ek here used
for the agent or instrument as often ( 3:18  9:2  18:1 ). See
 20:6,14  21:8  where "the second death" is explained as "the
lake of fire." The idea is present in  Da 12:3  Joh 5:29  and is
current in Jewish circles as in the Jerusalem Targum on  De 33:6 
and in Philo. It is not annihilation. The Christians put to death
in the persecution will at least escape this second death
(eternal punishment).