Therefore, be vigilant. For you do not know at what hour your Lord will return. (Mt 24:42)
γρηγορεῖτε οὖν, ὅτι οὐκ οἴδατε ποίᾳ ἡμέρᾳ ὁ κύριος ὑμῶν ἔρχεται.
Vigilate ergo, quia nescitis qua die Dominus vester venturus sit.
To be vigilant (γρηγορέω gregoreō)