Passage
For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
2 Thessalonians 2:7 (KJV)
Nearby Context
2 Thessalonians 2:5 Remember ye not, that, when I was yet with you, I told you these things?
2 Thessalonians 2:6 And now ye know what withholdeth that he might be revealed in his time.
2 Thessalonians 2:7 For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
2 Thessalonians 2:8 And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:
2 Thessalonians 2:9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
Study Lenses
The verse centers on "mystery", "iniquity", "doth", "already", "only", "letteth", "until", and "taken". It is saying that the verse draws attention to "mystery" and "iniquity", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 6's "And now ye know what withholdeth that..." into verse 8's "And then shall that Wicked be revealed...", so "mystery" and "iniquity" belong inside that flow. In 2 Thessalonians context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "mystery" and "iniquity" with trust shaped by these words, not by a vague optimism outside the passage.