Render thus: So that the community of thy faith [with other Christians, whom you may be able to serve] may show itself in act, causing full acknowledgment [from the world without] of every good work for Jesus Christ that is in you (Revised Version is not clear here); literally, may become working.
Not a theoretical or merely quiescent faith. He was to confess Christ before men (and see James 2:22). "For whatever good thing is in us makes manifest our faith" (Calvin). In you. Bishop Wordsworth reads ἡμῖν, "us"—the body of Christians, following A, C, D, E, K, L, with many Fathers and versions.