μεγάλα ὠφελήσεσθε πρὸς ἱστορίαν τῶν κοινῶν → that will be of great benefit to you in order to understand public affairs
ἑδραίως: ἐπίρρ. στερεῶς, ἰσχυρῶς, ἐπιμόνως, Ἡρωδιαν. 3. 14, 10 κλ.
firmemente