Zenit has just run an interview of Francis Cardinal Arinze, the prefect of the Congregation for Divine Worship and the Sacraments, published in Inside the Vatican magazine.
You should read it in its entirety, but here are some excerpts I thought you'd enjoy.
Regarding "music in the liturgy, we should start by saying that Gregorian music is the Church's precious heritage," he said. "It should stay. It should not be banished. If therefore in a particular diocese or country, no one hears Gregorian music anymore, then somebody has made a mistake somewhere."
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"The local church should be conscious that church worship is not really the same as what we sing in a bar, or what we sing in a convention for youth. Therefore it should influence the type of instrument used, the type of music used."
Suitability
"I will not now pronounce and say never guitar; that would be rather severe," Cardinal Arinze added. "But much of guitar music may not be suitable at all for the Mass. Yet, it is possible to think of some guitar music that would be suitable, not as the ordinary one we get every time, [but with] the visit of a special group, etc."
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Showmanship
"Vatican II brought many good things but everything has not been positive, and the synod recognized that there have been shadows," Cardinal Arinze acknowledged.
"There has been a bit of neglect of the holy Eucharist outside Mass," he said. "A lot of ignorance. A lot of temptations to showmanship for the priest who celebrates facing the people.
"If he is not very disciplined he will soon become a performer. He may not realize it, but he will be projecting himself rather than projecting Christ. Indeed it is very demanding, the altar facing the people. Then even those who read the First and Second Reading can engage in little tactics that make them draw attention to themselves and distract the people.
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Abuses not new
Contrary to what many think, he said, "even when there was the Tridentine Mass there were abuses. Many Catholics did not know, because they did not know Latin! So when the priest garbled the words, they were not aware of this.
"Therefore, the most important area is faith and fidelity to that faith, and a faithful reading of the original texts, and their faithful translations, so that people celebrate knowing that the liturgy is the public prayer of the Church."