He says that he volunteers at the homeless shelter as a way to 'atone for' [='make up for'] the sins of his youth.
(..) walks down that street. To die in the service of the gods would please each and every one of us. We yearn for it. But there is no call for it today. There will be no walk of atonement. Order up. Queen Margaery has already atoned for her sins by bringing another into the true light of the Seven. (..)2016 TvShow: Game of Thrones Title: Blood of My Blood Season: 6 Episode 6
(..) We'll be together again soon and everything will be better than it was before. Better how? Soon the... walk of atonement. He says there's no other way. Have you spoken to him at all, the High Sparrow? Yes, a few times. Have you? (..)2016 TvShow: Game of Thrones Title: Blood of My Blood Season: 6 Episode 6
(..) - Confess. Confess. It felt good. Beating me, starving me, frightening me, humiliating me. You didn't do it because you cared about my atonement. You did it because it felt good. I understand. I do things because they feel good. I drink because it feels good. I killed my husband because it (..)2016 TvShow: Game of Thrones Title: The Winds of Winter Season: 6 Episode 10