I hate to say it, but the ancient Slavs were so behind other civilizations that we can't even find any writings about their pagan religion.
Do you really hate to say it, or are you really happy to say it because you are a British/South African who comes to this forum to hassle Slavs and indulge in your stupid fantasy about how superior Western Europeans are to them?
Ancient Slavs were actually far ahead of other civilizations politically, because they refused to be governed by kings or other despots and instead lived on mirs
in which wealth was distributed equitably and everyone had their soveriegnty, unlike the craven ***** civilizations of Western Europe and Asia that bowed down to tyrants. When the proper human form of political existence, that of anarcho-syndicalism, is attained in the future it will be new for most of the world's cultures, but for Slavs it will just be a return to the superior lifestyle their ancestors enjoyed.
As for a lack of writing making the Slavs inferior, that is just ridiculous. Cultures whose stories are transmitted orally are in no way inferior to those with writing. In fact the memory of peoples without the crutch of script are far better, and that is why you see that the Slavs posting on this forum tend to be smarter than the others who come here.