Which have borne witness of thy charity before the church: whom if thou bring forward on their journey after a godly sort, thou shalt do well: Borne witness of thy charity before (in the presence of) the church - to stimulate others by the good example. The brethren so entertained by Caius were missionary evangelists (3 John 1:7). Probably, in narrating their missionary labours "before the church" where John was, they incidentally mentioned the loving hospitality, of Caius.
Bring forward on their journey - `if thou (continue to) forward on their journey,' by giving them provisions for the way.
After a godly sort, х axios (G514) Theou (G2316)] - 'in a manner worthy of God,' whose ambassadors they are, and whose servant thou art. He who honours God's missionaries (3 John 1:7), honours God.