3 John 1:3
For I rejoiced greatly, when the brethren came and testified of the truth that is in thee, even as thou walkest in the truth. For I rejoiced greatly, when the brethren came and testified of the truth that is in thee, even as thou walkest in the truth.
The joy expressed is great joy felt when brethren who were preaching the gospel to the Gentiles came and bore testimony that the truth was in Gaius and that he walked in the truth. Those visiting brethren were strangers and not men of influence. They were commended to Gaius for hospitality, with the request that they be received and entertained by the church of which Gaius was a member. To walk in the truth in this setting was to do faithfully whatever was done for the brethren and for strangers. That faithfulness included charity shown toward them which was witnessed before the church.
This rejoicing over those who walk in the truth stands in contrast to the discourteous course of Diotrephes. From self-superiority and love of preeminence he himself refused the brethren and hindered their reception. He went further to forbid those who would receive them and to cast such willing receivers out of the church, while also speaking maliciously against the writer. That example is not to be followed, for God's missionaries should always be given a kind reception.