LSJ
one must till the land, X. Eq. Mag. 8.8. τοὔργον ἔστ’ ἐ. it must be done or one must do it, A. Ch. 298, cf. E. Med. 791, X. Oec. 7.35 ; τὰ ἔργα… ὡς ἔστιν ἐργαστέα ib. 13.3 ; ὅτ’ ἧν ἐ. when it was necessary to act, S. Tr. 688.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)