What does 1 Corinthians 3:17 mean?

A rhetorical question in the previous verse established that the church in Corinth was God's temple, since the Holy Spirit lived in those believers. The same can be said of all local congregations: "the church" is the people, not a building, and those who are in Christ have God's Holy Spirit in them.

In that way, Paul declares that God is enormously protective of them. More specifically, God is protective of His own holiness. Since they are God's temple, and since God's temple is holy, they together are holy before God. Paul here elevates the value of the local church of believers in Jesus to the highest level. A group of born-again, saved Christians is something far above a simple gathering of like-minded people. That collective body of believers, not the buildings they meet in, is God's holy temple on earth.

Paul's main point, though, is this: If anyone destroys God's temple, God will destroy that person. He seems to have in mind not just those leaders who would build poorly on the foundation of Jesus, to use the metaphor from previous verse. Instead, Paul speaks of someone who would destroy the church altogether, perhaps with false teaching or by dividing the people instead of uniting them.

God will destroy that person. Does this mean He will end this person's physical life or that this person will be condemned eternally? Paul doesn't specify, but he clearly means to refer to God's harsh and painful judgment. A broader look at the New Testament shows that God might allow persecutors of the church to survive, for now, but all men will face eternal judgment for their conduct towards Christ and His church (Revelation 20:11–15).