Epistrophe is the noun form of epistrepho, meaning the act of turning — specifically conversion, the turning of a person from one way of life to another. It appears only once in the NT (Acts 15:3), describing the report of the 'conversion of the Gentiles' that brought great joy to believers as Paul and Barnabas traveled to Jerusalem.
The single NT use of epistrophe is charged with significance: the news of Gentile conversion caused 'great joy to all the brothers and sisters' as it was reported church by church. Conversion is public, shareable, joyful news — it is not merely a private inner transaction but an event that warrants communal celebration. Every epistrophe — every soul turning to Christ — is good news proclaimed. The church celebrates conversion because it is the visible fruit of the gospel, the evidence that God is building His kingdom from every nation.