The Greek adjective/noun ekdikos (from ek + dike, 'justice') means 'one who carries out justice' — an avenger or punisher. In 1 Thessalonians 4:6, it describes the Lord as the avenger of sexual sin. In Romans 13:4, it describes the governing authority as God's servant to execute wrath on the wrongdoer.
Ekdikos embeds the concept of divine justice into both eschatological and political theology. God is the supreme ekdikos — vengeance belongs to him (Romans 12:19; Deuteronomy 32:35). His delegated agents — governing authorities — carry out this justice in the present age (Romans 13:4). The personal call is not to be one's own ekdikos but to leave room for God's wrath. The certainty that God is ekdikos both restrains personal vengeance and provides profound comfort to the oppressed: injustice will not go permanently unanswered.