“To an unknown god”
For as I walked around and examined your objects of worship, I even found an altar with this inscription: TO AN UNKNOWN GOD. Therefore what you worship as something unknown, I now proclaim to you. (Acts 17:22–23 BSB)
What it sounds like today
A rhetorical flourish about an oddly labeled altar.
The cultural key
Such altars existed: Pausanias the travel writer mentions altars 'to unknown gods' on the road to Athens, and a famous story preserved by Diogenes Laertius tells how Epimenides once ended a plague by releasing sheep on the Areopagus and sacrificing wherever each lay down, on anonymous altars, insurance against offending a deity whose name nobody knew. Paul takes the city's humblest hedge, its admission of theological blind spots, as his opening. He then argues entirely from their own canon: 'In him we live and move and have our being' (attributed to that same Epimenides) and 'we are indeed his offspring' (Aratus, a Stoic poet), before turning the argument at the resurrection.
Recovered meaning
Paul preaches the Creator to Athens without quoting a single Hebrew scripture, building instead from the city's own altar and its own poets. The unknown god of their insurance policy is introduced by name, and the speech is still the model for translating the gospel into a foreign thought-world.