The verb diēgeomai means to tell a story fully or to narrate in detail. It is the root of diēgēsis — narrative — and appears in Luke and Acts especially, where eyewitnesses and apostles 'declare' what they have seen. Luke 1:1 references the many who had 'taken in hand to set forth in order a declaration' of the events.
The act of diēgeomai — full, detailed narration — is foundational to the Christian faith, which is grounded not in abstract philosophy but in historical events. Luke explicitly anchors his Gospel in eyewitness testimony and careful investigation. The disciples' full account of the Transfiguration (after Jesus's instruction to keep silence), and Peter's detailed narration of Cornelius's conversion to the Jerusalem church, show that the gospel advances through faithful, complete telling of what God has done.