1 Corinthians 16:9

θύρα. The use of the word θύρα in the sense of opportunity in the N. T. is noticeable. And it is further remarkable that it is not confined to any one writer. See 2 Corinthians 2:12; Colossians 4:3; Acts 14:27; Revelation 3:8.

καὶ ἐνεργής. This, combined with θύρα, is a somewhat bold metaphor. The result of the opportunity is here taken in conjunction with the opportunity itself. ἐνεργής is used in Classical Greek for productive, as for instance Xen. Oec. IV. 8 ἐνεργὸν (for the later ἐνεργῆ) οὖσαν τὴν γῆν καὶ πλήρη δένδρων. Here, however, we in English might say not altogether incorrectly, an effective opportunity, i.e. an opportunity for acting effectively. We may observe here also how these words of the Apostle corroborate Acts 19:19-20.