In III John 6, does this verse mean we can give testimony in the church? It's so compelling to make a point for denominational friends.
"Beloved, you do faithfully whatever you do for the brethren and for strangers, who have borne witness of your love before the church. If you send them forward on their journey in a manner worthy of God, you will do well, because they went forth for His name's sake, taking nothing from the Gentiles" (III John 1:5-7).
John is saying that brethren who have visited Gaius, have publically told brethren in their own churches about Gaius' hospitality. This is not like the denominations who talk about their own lives and call it witnessing for God.