Albert Barnes Commentary 3 John 1:5

"Beloved, thou doest a faithful work in whatsoever thou doest toward them that are brethren and strangers withal;" — 3 John 1:5 (ASV)

Beloved, you do faithfully. In the previous verses, the writer had commended Gaius for his commitment to truth and his general uprightness in his Christian life. He now speaks more specifically of his acts of generous hospitality and says that he had fully, in that respect, done his duty as a Christian.

Whatever you do. This applies to all your dealings with them and all your conduct toward them. The specific thing that led to this remark was his hospitality, but the testimony regarding his general conduct was such as to justify this commendation.

To the brethren. This probably refers to Christians who were well known to him—perhaps Christians in his own church.

And to strangers. This refers to those who had gone to the church where he was a member, carrying a letter of commendation from John. See Romans 12:13 and Hebrews 13:2.