3 John 5 New English Translation

⁵Dear friend,^[a] you demonstrate faithfulness^[b] by whatever you do for the brothers (even though they are strangers).

3 John 1:5 tn The author has already described Gaius as “dear friend” or “beloved” (τῷ ἀγαπητῷ, tō agapētō) in v. 1; he will address Gaius in the same way in vv. 5 and 11 (᾿Αγαπητέ, Agapēte). This is a term of endearment and personal warmth, much as it is when used by the author as an address in 1 John 2:7.
3 John 1:5 tn BDAG 821 s.v. πιστός 1.b offers the translation “act loyally” for this context, a usage which is not common but does fit well here. Since the author is going to ask Gaius for additional help for these missionaries in the following verse, he begins here by commending Gaius for all that he has already done in this regard.sn When the author tells Gaius “you demonstrate faithfulness by whatever you do” he is commending him for his faithful service to the traveling missionaries (the brothers). Gaius has assisted them, and they have now returned with a report of this to the author (3 John 3).

New English Translation (NET)