{Gaius my host} (Gaios ho xenos mou). Perhaps the same
Gaius of  1Co 1:14  ( Ac 19:29  20:4 ), but whether the one of
 3Jo 1:1  we do not know. Xenos was a guest friend, and then
either a stranger ( Mt 25:35 ) or a host of strangers as here.
This Gaius was plainly a man of some means as he was the host of
all the church. Erastus ( 2Ti 4:20 ) was "the treasurer of the
city" (ho oikonomos t(8873) pole(9373)), one of the outstanding men of
Corinth, the "steward" (house-manager) or city manager. See  Lu
12:42  16:1 . He is probably the administrator of the city's
property. {Quartus} (Kouartos). Latin name for fourth.