The use of organs in the Western Church can be a confusing thing. As a historian and church musician, let me make the following statement. First of all, the organ itself was actually invented by the Byzantines. It was used for public entertainment in the Hippodrome in Constantinople, in much the same way as a ball park organ is used at a baseball game in the USA today. However, that was about all the Byzantines ever did with it. It was looked upon as a rude, vulgar instrument suitable for entertaining crowds at circuses and horse races. It was not viewed as an instrument appropriate for the Church. The Latin Church in the West shared EXACTLY this same view of the organ before the year 800. However, after Charlemagne was crowned Holy Roman Emperor in Aachen (Germany), he began to express an interest in getting an organ similar to what the Byzantines had. So Germanic people traveled to Constantinople, studied the organ technology, and brought that technology back to Germany (the Holy Roman Empire at the time). Charlemagne still did not want the organ in the Church. He simply wanted it for public entertainment like the Byzantines. The interesting thing is that almost no one else except Charlemagne showed any interest in the organ in the West at this time. Rome and the Pope would have none of it. They preferred Gregorian chant. Spain, France, and England didn't like the idea either. So the Masses in all those countries continued to be chanted unaccompanied. Even in the Germanic lands, it took HUNDREDS of years for the organ technology to develop. Church organs themselves were not invented in Germany until around 1400, well after the schism between Rome and Constantinople. And it wasn't until about 1500 that the organ became widely used in Germany. Even then, it was NOT to accompany the singing of hymns, because THERE WERE NO HYMNS. The Mass was in Latin. Hymns (in terms of rhyming prose in the vernacular) are a product of the Protestant Reformation, not the Roman Catholic Church. In Germany in the 1500s the organ was used in a VERY LIMITED way during the Mass. It would play quietly before Mass started, during the Consecration (which the priest said in a low voice) and after the Mass was over. That's it. It still did not play while anyone was SINGING. Singing was ALWAYS unaccompanied, even then. It was not until Martin Luther came along that the organ was introduced to accompany the singing of hymns and parts of the liturgy. And even then, the organ's influence was contained mostly in northern Europe: Germany, the Netherlands, England, the Scandinavian countries, and France. Europe south of the Alps was (and still is) somewhat suspicious of the organ in Church. If you recall the funeral of John Paul II, the organ was scarcely used at all. Nearly all of the singing was a capella, which (by the way) is the way the Vatican still prefers it. But it does ALLOW the use of the organ. Rome, however, has never mandated that the organ must be used. It is a local decision.