John, Third Epistle of

is addressed to Caius, or Gaius, but whether to the Christian of
that name in Macedonia (Acts 19: 29) or in Corinth (Rom. 16:23)
or in Derbe (Acts 20:4) is uncertain. It was written for the
purpose of commending to Gaius some Christians who were
strangers in the place where he lived, and who had gone thither
for the purpose of preaching the gospel (ver. 7).

The Second and Third Epistles were probably written soon after
the First, and from Ephesus.