Expositor's Bible Commentary Commentary 2 Thessalonians 2:7

"For the mystery of lawlessness doth already work: only [there is] one that restraineth now, until he be taken out of the way." — 2 Thessalonians 2:7 (ASV)

Further clarification (“for”) is in order. The “secret power [lit., “mystery”; GK 3696] of lawlessness” was already evident in such things as their own persecutions (1:4), but lawlessness will be open when the rebellion arrives and the lawless one is unveiled (2:3, 8). The secrecy and limitation are attributable to "the one who now holds it back.” Upon his removal, the rebellion will break out.