The objection is that "the episcopal state is more perfect than the religious state. But bishops may have property, [so] religious may also."
And St. Thomas begins his reply with the words:
The episcopal state is not directed to the attainment of perfection....
Which explains plenty.
I suppose he could have ended his response right there, leaving us to speculate at what unwritten words might have been spoken between author and secretary before they moved on the respondeo ad sextum. But to clarify his point, he continued:
...but rather to the effect that, in virtue of the perfection which he already has, a man may govern others....
It would be catty to add, "Which explains even more." So I won't.
Still, this idea -- you might even call it an ideal -- of the episcopal state suggests two things: First, the Church is in need of a steady supply of perfect candidates to become bishops. Second, if by chance a diocese winds up with a bishop who is less than perfect, the people of that diocese shouldn't expect him to attain to perfection in the execution of his office; if they want him to become perfect, it'll probably take prayer and fasting on their part to help him along.