The Book of 3rd John
"you are walking in truth"

Bible Study and Commentary
James Deering,

conjunctions & prepositions underlined, words not in original text in italics)  (alternate text in purple)

3 John :3
I was very glad when brethren
        came and
        bore witness to your truth
    that is,
        how you are walking in truth.

3 John :4
I have no greater joy than this,
    to hear of my children walking in the truth.

This verse, introduced with the preposition for, tells us the reason for Johnís love and prayers for Gaius. It is because Gaiusí life was such that it became the subject of the witness of Johnís friends and brethren. It would seem from the wording that these friends and brethren made it a point to seek out John just to tell him of Gaiusí truthful life. His lifeís witness was that he was a man of Godís truth, and that not only was he a man of Godís truth, but that he walked in that truth everyday.

John reckons Gaius as one of his "Children." This could mean that he was especially fond of him, proud of his relationship with the believers there, or that he could have actually been one of Johnís personal conversions to Jesus Christ. Whatever the relationship John shares the pleasure of love that comes from seeing others who labor "in Christ" and "walk in the truth."