The fanatical despotism of Ivar the Boneless is driven by flames. He not only sets himself up up as a divine god with his henchmen executing his enemies, his own delusional statue and public human sacrifice of his rivals, fire is repeatedly depicted as the agent of his authority. He burns a women purporting it to be Lagertha and his men mark and burn anyone who stands against him. Yet Ivar goes one stage further, attempting to eradicate the traditional order of fate itself, manifest in the series through the prophesies of the Seer. As previously stated, I suspect this is an extended reflection on fascist governance, behaviours and thought in the contemporary world, more than anything to do with Norse legend and history.
So when Ivar kills the Seer in his hut, and then denies people access to the circumstances of his demise, he is attempting to curtail the unravelling of history itself and set himself up as an eternal ruler in denial of past and future. He then burns the Seer’s body in the woods in secret on a small (utterly ineffective) pyre, with only his loyal bodyguards in attendance. Ivar watches from the back of a cart: seemingly keen to ensure the Seer is fully and finally gone for good.
Fire is thus a method of concealment and mnemonic destruction. Fate itself is being negated. I admit, the depiction is crudely a spin off the treatment of malign ghosts (draugr) in Icelandic sagas, such as Glam’s body in Grettir’s Saga. But in the context of the story line of Ivors fascist reign, this Season 5 of Vikings fire is a mechanism for the eradication of dissent and destiny rather than sacral transformation.