Satan ignored Sloth, and ignored his struggling. The ropes would hold.
The ring finger proved a little tougher to saw through, and Satan decided to break Sloth's middle finger just as a precaution before he started cutting. By the time Satan was done, the table was slick with Sloth's blood and three of the Sin's fingers had been sliced off of his hand.
"There!" Satan said cheerfully, leaning over Sloth. "Not so bad, was it? And shhh, now it's over." He ran a blood-covered hand through Sloth's hair. "I know that you only wanted to help your sister. But if Lucifer and I can't have your loyalty, we at least require obedience. Now, do you want me to kill you?"