At any rate, Christian theology developed intricate theories to match things like the veneration of saints, relics, icons and what not into what is theoretically supposed to be monotheistic religion. Personally I don´t see what worshipping bones, bits of cloth, pictures and other ´sacred´ objects has to do with God, but then I´m not a Christian.
Christians don't worship those things - they venerate them - and that's not the same thing.
Still, it seems to me that monotheism has an inherent tendency to develop into something like a de facto polytheism. It happened in Judaism in the intertestamental period too. I don't see any reason to suppose that the development of icons, relics, and so on in Christianity had anything to do with pagan influence - I think it can be explained perfectly adequately in terms of Christianity's own internal logic, including the ideas it took over from Judaism.
(It's also the case that polytheism often seems to have an inherent tendency to develop into monotheism, too, which is equally interesting.)
Wait, I'm confused. I thought it was pretty well established that Christianity built upon existing religious traditions when it came to a new area, which is why we have Easter and Christmas on major 'pagan' holidays, along with several other parts
It is more complicated than that. First, sometimes Christianity has done that, and sometimes it hasn't. Different Christian missionaries have adopted very different attitudes to local traditions in different times and places. Compare e.g. the attitudes of Jesuit missionaries to China in the seventeenth century with those of British missionaries to Africa in the late nineteenth century.
In the case of the Christianisation of Europe, it's true that some pre-Christian traditions were incorporated into Christianity, such as the building of churches where temples had once stood (although I think this was less extensive than is often supposed). But others were not, such as the veneration of trees, which people like Boniface spent a lot of time cutting down. Festivals are a particularly difficult issue. I don't know of any good evidence that Christmas directly corresponded with any pagan festival, although it was obviously at around the time of Saturnalia and Yule. It coincided with Sol Invictus, but that itself was a late introduction to Rome and wasn't relevant to northern Europe. John Chrysostom says that he thinks Christmas was given the date it was so that the Christians had something to do while everyone else was recovering from Saturnalia and preparing for New Year, and that seems as good an explanation as any to me. Easter is even harder to pin down. It's often said that the very name "Easter" comes from a pagan goddess who was celebrated at this time - but what's less often said is that we know of the existence of that goddess only from a single reference in Bede, and we know pretty much nothing about her or the celebrations. I'm sure that a lot of pre-Christian elements got incorporated into the Christian festivals, but beyond that it's mostly speculation.
