Religion
No religion survived the end of the world wholly intact. Some saw it as God's judgement, and that the end times had come. Others saw it as proof that there was no higher power looking out for mankind, and abandoned their faith entirely.
The powers of the major denominations of Europe are gone, and any organization left is on the individual priest level. Many priests have in fact developed their own heresies to explain the end of the world, and may be preaching sermons unrecognizable to the faithful of years prior.
Some survivors, bolstered by the whispered tales of strange phenomenon witnessed in the frozen wastes, have taken up the folk superstitions of their grandparents, leaving offerings to half-remembered old gods.
Others have turned to older, darker paths, seeking truth and esoteric knowledge.
Mysticism is the skill that uses faith and belief to empower characters who act as spiritual guides, prophets, or keepers of doctrine. Whether the abilities it grants are psychosomatic or truly supernatural is left for you to decide.