I was glad to see Athelstan return... and I was also happy that Ragnar told him he wanted him to come back. Athelstan may be struggling with religion, but through it all he can see one thing clearly... As a monk he was a slave, under Ecbert he was a slave, threatened with death.... but with Ragnar he is a free man. Ragnar respects him... it goes back to when he left him in charge of his kids while he and Lagertha went on a raid. He saw Athelstan's moral standards and trusted him... respect came after... perhaps Ragnar is Atheist as well? Its hard to tell because the series visually despicts that both religions are alive between Athelstan's Christianity allusions and Odin's crows. Ragnar at the least has a more liberal view on the gods... this became evident when he asked Athelstan on this faith and replied that he wished for his gods and Athelstan's god to be friends one day. Ragnar is looking outside the box and this is what is causing Floki to lose respect for Ragnar on the surface.... but you never know with Floki.