I’d say that the end of that verse is the parenthesis that the submission is to occur within. Ready (submission) to do what is good.
Irenaeus said it like this 180 AD ish.
Irenaeus book 5 xxiv
2. For since man, by departing from God, reached such a pitch of fury as even to look upon his brother as his enemy, and engaged without fear in every kind of restless conduct, and murder, and avarice; God imposed upon mankind the fear of man, as they did not acknowledge the fear of God, in order that, being subjected to the authority of men, and kept under restraint by their laws, they might attain to some degree of justice, and exercise mutual forbearance through dread of the sword suspended full in their view, as the apostle says: "For he beareth not the sword in vain; for he is the minister of God, the avenger for wrath upon him who does evil." And for this reason too, magistrates themselves, having laws as a clothing of righteousness whenever they act in a just and legitimate manner, shall not be called in question for their conduct, nor be liable to punishment. But whatsoever they do to the subversion of justice, iniquitously, and impiously, and illegally, and tyrannically, in these things shall they also perish; for the just judgment of God comes equally upon all, and in no case is defective. Earthly rule, therefore, has been appointed by God for the benefit of nations, and not by the devil, who is never at rest at all, nay, who does not love to see even nations conducting themselves after a quiet manner, so that under the fear of human rule, men may not eat each other up like fishes; but that, by means of the establishment of laws, they may keep down an excess of wickedness among the nations. And considered from this point of view, those who exact tribute from us are "God's ministers, serving for this very purpose."
Unjust judges and magistrates who are not dealt with bring the wrath of God on the whole nation.