See on 2Ti 2:14, and see on ὑπόμνησιν reminding, 2Ti 1:5.
Principalities and powers (ἀρχαῖς ἐξουσίαις)
Omit and. Principalities which are authorities. Ἁρχή beginning = that which begins: the leader, principality. See on Col 1:16; see on Jud 1:6; see on Act 10:11. Only here in Pastorals. Ἑξουσία right, authority. See on Mar 2:10; see on Joh 1:12; see on Col 1:16. Only here in Pastorals. For the combination principalities and powers, see on Luk 20:20.
To obey magistrates (πειθαρχεῖν)
Comp. Act 5:29, Act 5:32; Act 27:21. See on Act 5:29. The idea of magistrates is contained in the word itself; but it is quite proper to render as Rev. to be obedient. Rare in lxx.
Ready to every good work (πρὸς πᾶν ἔργον ἀγαθὸν ἑτοίμους εἶναι)
The phrase N.T.o. Ἑτοίμος ready, only here in Pastorals. Comp. ἑτοιμασία readiness or preparation, Eph 6:15 (note).