A.T. Robertson Commentary Revelation 2:11

"He that hath an ear, let him hear what the Spirit saith to the churches. He that overcometh shall not be hurt of the second death." — Revelation 2:11 (ASV)

Shall not be hurt (ου μη αδικηθη). Strong double negative with first aorist passive subjunctive of αδικεω, old verb, to act unjustly (from αδικος), 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 (εκ του θανατου του δευτερου). Εκ 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; John 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).