While the priesthood allows for a greater capacity for grace, and therefore reward, it is still contingent on the individual to make use of that capacity. A priest who ends up in Hell is far worse off than any average saved soul in Heaven.
- So each person's response to grace is just as important, for even if your vocational state allows for great grace, if you don't avail yourself of that grace how does it profit the person?
Think of it this way, a priest is given a Ferrari, but he is tottering along in the breakdown lane, while little old ladies are passing him in their old Fords from yesteryear. The parable of the talents teaches us the same lesson: To whom much is given, much is expected, (Luke 12:48) so, accordingly the responsibility is great.
So in the end, we ought to maximize our response to grace for that will assure the highest state of perfection, and help to even expand our capacity for more.