Doctrinally speaking, and perhaps above and beyond anything else, the Koran is still the primary unifying factor in Islam. We are tempted to compare this with the role of the Bible in Christianity but that is a misleading comparison, as we’ve already noted. For one thing, the Bible in Christianity is never authoritative, but rather it is a particular interpretation of the Bible that is authoritative, and as the centuries have demonstrated, it is never entirely clear to the great mass of believers how the Bible can be interpreted. Hence the magisterium, which gives unity to the Catholic world, and its absence, which gives perpetual disunity to the Protestant world. A more accurate comparison here, then, is to compare the Koran with Christ, since whatever else Christians fight about amongst themselves, the fundamental belief that Christ died for the sins of man, and that Christians are saved through faithfulness to Christ, is almost never in question. So we can say that the unity given to Christianity by Christ (and not by the Bible) is the unity given to Islam by the Koran.
This is helped by the fact that the Koran was given in the Arabic language and so although there are certainly difficulties the believer may face when interpreting it, it is obvious that they will not face the same set of difficulties that Christians face when they pick up a book that has been thrice translated and was originally given in a context that has few similarities to their own. It is in this sense that we might suggest that the Koran’s meaning is, at least to a agree, more immediately apparent to Muslims than the meaning of the Bible is to Christians, and for this reason it can function more as a unifying factor than a dividing one.