Brit Mila means oath of the word.
Why does it take place "down there" where not a word comes out?
Josef and Rabbi Nachman are the purest of the pure right? Why is that?
What if I told you that had Moses not chosen three days we would never have received the Torah and by the way the erev rav got it as well, you know why we got it? ONLY BECAUSE MOSES made the right decision. In fact we have a de-facto Chazaka that we don't "need" sexual lust.
So what does Josef and Nachman have to do with this?
We made an oath to Josef and we didn't keep it. Rabbi Nachman is our chance to keep it. Since the oath is by us to them, they have no part in breaking this oath only we do!!!
That explains why it is a spoken oath which they have not blemished, but we in fact have done so!!!