Tanrak believes in God because he needs to believe that his parents are in heaven waiting for him. That’s why he can’t believe in ghosts, can’t admit he’s afraid of them. Because then his beliefs are wrong and his parents are really gone. He’s walking through the cemetery forcing himself to believe that these people are not in the graves but, through sacraments like baptism (John the Baptist), are actually in a better place. He’s laying six feet under ground in a dried out pool (no baptism option here) telling Barth his parents’ souls are saved. Then soon enough, if he can live purely, he’ll be reconciled with them. Graves and ghosts, those signs of death, are pervasive in the series, but it hurts Tanrak too much to accept that death might really be the end, that he’ll truly never get to be reunited with them.