"Returning to his studies in Uppsala, Bo Giertz was mentored by New Testament exegetics professor Anton Fridrichsen; he later declared that all his books had been written in an endeavour to disseminate what Fridrichsen had taught him, ideas which he believed to be in marked contrast, for instance, to the efforts of German theologian Rudolf Bultmann to demythologize Christianity of accreted concepts of angels, demons, miracles, heaven and hell — all of which Bultmann considered as significant barriers to people's understanding and accepting the inner message of Jesus.