I was told by a friend it was not and that it is, in fact, a sin. I don’t think I am doing anything wrong. The priests and bishop I’ve asked all tell me it is permissable for me to play for Protestant services on Sunday. They applaud my attempt to evangelize in this way.
So long as you are meeting your Sunday obligation at Mass and are not receiving Protestant communion, which are required of Catholics, I would say it is more a matter of prudential judgment whether you should participate in Protestant services in this manner. Let’s look at some of the considerations:
[list]What music are you being asked to play?[/list]
Some Protestant music is unobjectionable from a Catholic perspective. But where it is objectionable because it promotes doctrines that differ significantly from Catholicism, it is problematic (e.g., “Amazing Grace,” “Blessed Assurance”).
[list]Are you volunteering your time or are you performing a job for which you are paid?[/list]
If it is a part of your livelihood to play the music set before you by paying customers, performing for Protestant congregations is not problematic. Volunteering, on the other hand, suggests that you as a Catholic are helping this church promote not only the truths that it holds that mirror Catholic teaching but also those understandings of the gospel on which we disagree.
[list]Are you yourself actually being evangelized away from your Catholic faith by the churches where you perform?[/list]
Direct proselytization is easy to spot and shrug off; subtle, perhaps even unattempted, evangelization is not. It would be very easy to begin comparing the Protestant services at which you perform with Catholic services and begin to feel Catholic services are lacking. As you form friendships at these Protestant churches that you are only able to pursue when you’re there, it can become easy to neglect your Catholic duties in favor of the fellowship you find elsewhere.
[list]Finally, are you also offering your talents within the Catholic Church?[/list]
Your first obligation is to offer the talents God gives you for the Church he founded and the public worship he specifically ordained: the Mass. If you are not already involved in music ministry in your local diocese, perhaps you might consider becoming involved. If music ministry in your parish and diocese eventually supplants the time you’re able to offer Protestant churches, then that’s all to the good. Perhaps you can simply restrict your outside playing to specific ecumenical events co-sponsored by Catholic and Protestant churches.