Buddhi that becomes pure when you listen to a Sat Purush , or the Gnani purush, it is called avyabhicharini buddhi (intellect that takes you towards your Self). All these people have deluded intellect. Lord Krishna said that you will need avyabhicharini buddhi ( vyabhicharini buddhi ) is deluded intellect. Everyone in the world has deluded intellect, which is constantly harming him or her. Not for a second are they doing good for themselves. They believe the deluded buddhi to be the right buddhi !