Is it hard yet? Good slave. Now, keep stroking it at a medium pace.
I remember when you first came under My wing, I had to keep you in a chastity belt. But as time went on I started removing your belt for longer periods of time, to see how it would work.
It was not without slip-ups, of course. But each time you came without permission I exacted such swift and painful punishment on you that it reinforced the idea of staying chaste. And, of course, I put you back in that chastity belt for a while whenever that happened.
Why don't you think about what kind of punishment I used to give you for cumming without permission? Think about it for the next minute, and keep stroking at the pace I told you to.