Albert Barnes on Titus 3:1

Put them in mind to be subject, etc. See the duty here enjoined, explained Rom 13:1, seq.

Principalities and powers. See these words explained Rom 8:38. The word here rendered powers, (εξουσιαις,) is not, indeed, the same as that which is found there, (δυναμεις,) but the same idea is conveyed. Comp. Eph 1:21.

To obey magistrates. That is, to obey them in all that was not contrary to the word of God. Rom 13:1, seq.; Acts 4:19, Acts 4:20.

To be ready to every good work. To be prepared for (ετοιμους); prompt to perform all that is good. Php 4:8. A Christian should be always ready to do good as far as he is able. He should not need to be urged, or coaxed, or persuaded, but should be so ready always to do good that he will count it a privilege to have the opportunity to do it.

(a) "subject" Rom 13:1