I sometimes hear people exhorting our return to a version of Christianity less tainted by modern culture and influences, as if there were a moment when the undefiled faith was easily discernible as directly revealed by God. An understanding of history (or even a broad reading of the Bible) will quickly unravel the supposition that this might ever be possible. The history of both Christianity and Judaism repeatedly demonstrates how religions are influenced by and adapt to surrounding cultures - sometimes in acquiescence to those cultures, sometimes in rebellion against them.
There is no single moment in time, to which we might long to return, when Christianity has been perfect. The Christian faith is continuing to evolve, as it must, along with the times and places in which Christians exist. Christianity today varies significantly, not only from denomination to denomination, but from country to country. The questions that inevitably arise from this situation become 'is there a core that must not change?', 'what is that core?', 'how do we discern it?'. This is where disagreements often arise as people mistake doctrines that are only a couple of centuries old for ones that originated with Jesus. Any search for the authentic core of Christianity must take into account the history of the church across cultures, the quest for the historical Jesus and the development of Judaism.
In most cases, the result will be something simple like love God and love your neighbour.