The Greek word is phtheiro and means “to destroy by corrupting.” It is used here first (If any man destroys the temple …) as having to do with marring and scarring an assembly by unprofitable, impure teaching which leads to a partisan spirit thus causing divisions in the assembly, and also leads believers away from holiness into carnality.
Secondly, the word is used to point out the marring of the offender by God through divine retribution: (Him will God destroy …).
Paul is not telling us in verse 17 that God will destroy us and damn us in the lake of fire if we do something unbecoming to a Christian, something which dishonors God instead of honoring Him. The same truth is pointed out here as in verse 15, concerning a man’s stewardship being burned but his spirit saved. One Greek authority translates this verse thus: “If any man do hurt to the temple of God, to him shall God do hurt.” — Greene, pages 146-147.
holy (v.17) = separated — from sin and unto God
Several of my commentaries (including Greene above) state that the temple in view in verse 16 is the local church and that the Corinthians were being warned against defiling it with divisions or faulty teaching. I’m not sure I’m convinced. The verses immediately before and after this passage refer to individual Christians (and specifically those who teach and those who honor the teacher over the truth). The context is the church at Corinthians, yes, but it’s individuals who are being warned to be careful of their motives and priorities. I think the “temple” here is the individual and the warning is to his work in the church. But I could be wrong.