What Does It Take?
Obviously, when someone is chosen to direct or perform music for the liturgy, the first consideration is musical ability. (OK, maybe sometimes availability is a prior concern, but let's hope that musical ability is important to your superior too.) But that's not the only thing that determines whether or not you do the job well. There's another quality, beyond musical ability, that is crucial to your future as an excellent liturgical musician - I call it Game.
Whether you're the organist, the choir director, the cantor, or a single soprano in a vast sea of sopranos, to some degree you have taken a step to put yourself out there. Congratulations! It's a leap of faith, and it can be hard to make! The further out front you are, the more obvious it is when you make mistakes, as everyone inevitably will. You can insulate yourself from fear a little by being prepared, but you have to acknowledge at the outset that You Will Make Mistakes And People Will Notice. The only way to survive in liturgical music ministry is to accept this and be willing to try anyway.
Preparation is important, don't get me wrong! It's definitely your duty to be as prepared as you can reasonably be, and to know your abilities and their limits. But I would always rather have an organist who can make super loud mistakes and then continue on like nothing happened than a timid organist who never makes mistakes, but never tries something new. Why? Because preparation alone can never be sufficient; there are too many variables when more people are involved. The more people, the more variables - and often, the most important liturgies have most people involved, not to mention extra elements to throw you off.
Sometimes, things go wrong and you need to make a snap decision - usually related to the timing of something, which no amount of preparation can cover. Sometimes, things go really, really right and you get a flash of inspiration - grace? - and you just need to see what would happen if you tried this and it's awesome. Maybe your cantor is having a really great day, and the moment just seems right to throw that 32' reed stop in the pedal; or maybe an alternative meditation piece that your choir knows well enough matches the homily so much better than the one you planned on. If you don't have Game, these flashes of inspiration are mere distractions to be dismissed, rather than opportunities to be seized.
If you're managing other musicians, you need to train your musicians in the Way of Game as well, or else the amount of Game you have almost doesn't matter, because changing plans will throw them into a panic. Try to remember that training is what happens in rehearsal, though - respect their comfort levels. Allow newer musicians to observe the veterans successfully changing tack in the liturgy before asking them to do the same. And always, always, be a good communicator. Make sure everyone knows your special hand signals (I have a set for "continue on," "go back to the beginning," and differentiating the one-handed sign for v1 from v6, v2 from v7, etc). Deliver changes of plans separately to each section. Write things down. My choir loft has a large dry-erase board, on which I write the order of all the things we are singing - changes are written in red. I also keep plenty of pencils and post-it notes on hand. Choose your moments to communicate things to others - respect the primacy of the Gospel by not interrupting it; if you have to speak something, try to cover by doing it while the Creed is being recited, or the Our Father. Otherwise, do it in writing.
God gave you talent, opportunity to develop it into a skill, and a situation in which you can put your skill to use in His service. Don't doubt that He will also take your work and make of it something bigger than you can do on your own! Sometimes, He will choose to allow you to learn humility - thank God for those moments too. But make it your practice to open yourself up to do His work. Pray, Stretch, and God's Will Be Done.
This post is dedicated to Andrew, the Gamest Gamer my choir has ever had, to whom we owe the rehearsal term "Andrew's Train Wreck," but also the push behind a great deal of our musical growth. You will be missed more than I can ever say, even with music. I hope you come back to us.