ἐπέμψατε ἀγγέλους τοῖς ἀλλήλοις ὥστε ἔγνωτε τὸν κίνδυνον → you sent messengers to one another so that you knew the danger
χρῆσται: ἴδε ἐν λ. χρῆ (ἢ χρή).