There is a persistent strain in Christianity and Islam which emphasises that the nearer to the source, the purer the water; in both faiths we have seen, and we see, a search for ancient practices and belief. But the assumption behind this belief needs questioning, resting, as it does, on questionable assumptions.
The first of these is the notion that we can, in fact, extract a clear idea of ancient practice and belief from the surviving sources. Those scholars who have questioned whether there was in fact any concept of orthodoxy in the ancient church have emphasised a plurality of practice and implied something similar about belief; I am not entirely in agreement with them, but they have a point. We can construct only from what survives, and what survives will not give us a picture of everything, and even if it did, it would include much that is not orthodox. We could, of course, relive old arguments about Arianism, but on the whole I would advise against it (not least since there are ways in which we often rehearse them).
The second assumption to be questioned is the idea that what is older is purer in some way. Any history of heresy will tell you that heretical ideas go back to the beginning – we can see St Paul criticising them, and SS Peter, John and Jude all warn about those teaching incorrectly; from the beginning understanding and misunderstanding are mixed.
The third assumption is the one that implies that later is somehow more corrupt. This depends on a further assumption, which is that the Apostles understood the fullness of the relevation of Christ; there seems little evidence that this was the case. The assumption seems to be that at Pentecost the Apostles received not only the inspiration of the Spirit to speak in tongues and to go out as missionaries, but that they had a ful understanding of the nature of God as Trinity, and of Jesus as wholly-human and wholly-divine. If that were so, it was forgotten at once, as otherwise, when various heretics advanced what turned out to be misunderstandings of these things, the early Church would have cited Apostolic testimony to disprove them; this did not happen. Instead, the church did the hard work of trying to reach agreement on verses from Scripture which could be, were, and still are, read in different ways. Would it really be such a good idea to abandon these advances in understanding? On what ground, given the questioning of the various assumptions embedded in the argument that older is purer?
We are the inheritors of a rich and varied tradition of Christian practice and belief. No doubt we inherit some bad things and some good, but we should take care not to discard what is old simply because it is not new. To trespass on Catholic grief, it seems to me that this was one of the problems with the way Vatican II was interpreted; those who wanted to make all things new because they disliked the old, used it as an excuse to do something they already wanted to do. There was a similar development in Anglicanism in this country which I regret hugely – the abandoning of the Book of Common Prayer.
What is old and still works is sanctified by the use of our ancestors; we should not lightly abandon their heritage in pursuit of a mythical past.