What is the explanation of the following hadith?
It was narrated from Jaabir (may Allaah be pleased with him) that the Messenger of Allaah, sallallaahu 'alayhi wa sallam, said of the Jahannamiyyoon (those who will have been in Hell) that they “would be brought forth from the Fire after having been in it. They will come out as if they are branches of sesame. Then they will go into one of the rivers of Paradise, where they will wash themselves, then they will emerge like sheets of paper.”
Why are they compared to sheets of paper? Does it mean that they are free of impurity?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

Imaam An-Nawawi explained this hadeeth, which was narrated by Imaam Muslim, and clarified why the Prophet compared them to sheets of paper. He wrote:

“The word sesame refers to the well-known sesame from which sesame oil is extracted. Imaam Abu As-Saʻaadaat Al-Mubaarak ibn Muhammad ibn ʻAbd Al-Kareem Al-Jazari, who is known as Ibn Al-Atheer said, 'What it means – and Allaah Knows best – is that if the branches of sesame are gathered and left in the sun so that their seeds may be collected, they turn thin and black as if they have been burned, so these people are likened to them.' The hadeeth also reads, 'then they will emerge like sheets of paper.' They are likened to sheets of paper because they will be so white after they wash themselves and all the blackness that was on them is removed.” [Sharh Muslim]

Allaah knows best.