In the New Testament, too, Paul describes the body of a Christian as the temple of the Holy Spirit, so we should honor God with our bodies. It’s the same passage where he says, “shall I take the members of Christ and unite them with a prostitute?” Back when I used to cut that was the passage they used against me. Self-destructive behavior is not condoned by God.
What this means regarding lots of saints’ expression of faith by hurting themselves (like st. Rose of Lima or in my parish, Conchita, who founded the Missionaries of the Holy Spirit and branded Jesus’ name on her chest) I don’t know. I will say there is a probably a fundamental difference between pain for pain’s sake and suffering in order to grow in faith.