ἐπ' αὐτὸν ἥκεις τὸν βατῆρα τῆς θύρας → you've come to the crux of the matter, come to the point, hit the nail on the head, you've come to the very threshold of the door, you are come to the very threshold of the door, you've arrived at the truth of the matter
measureless: P. ἄμετρος, Ar. and V. ἀμέτρητος.
boundless: P. and V. ἄπειρος, Ar. and P. ἀπέραντος, V. μυρίος (also Plato but rare P.), Ar. and V. ἄβυσσος.
hard to understand: see inexplicable, obscure.
