Every couple of weeks I sing with an evensong chorale, singing Gregorian chant and other liturgical music for a meditation service at one of our local churches. The whole experience is deeply spiritual for everyone who comes, including (and especially) the singers. Over the past few years we have focused on how to collaborate on a level that befits the experience we are trying to generate for the congregation. And it really comes down to sustaining flow. Our director Alison Nixon, who thinks a lot about these things, usually has some wisdom to impart to us each week. On Sunday …