According to the common faith (κατὰ κοινὴν πίστιν)
The phrase N.T.o. Κοινός common, usually in contrast with καθαρός pure or ἅγιος holy, as Act 10:14; Act 11:8; Rev 21:27. In the sense of general as here, Act 2:44; Act 4:32; Jud 1:3. Comp. 2Pe 1:1. The “catholic” faith. Κατὰ according to, as Tit 1:1.