The trick is to introduce new music a little at a time and let the choir's appreciation of it grow as they get acquainted with it. People like what they know. That is an acknowledged fact, so just work with it. You could tell an interesting story about how it was written or who wrote it. You could have some recording played or an accomplished singer perform it for the group. You can share your personal, spiritual connection to it. But most important, allow enough time to learn it in stages. Even good sight-readers may be able to perform it quickly, but they won't remember it or have a connection with it unless given enough time to internalize it.
One of the hardest parts of learning a new piece is keeping all of the parts together. Even if the singers are singing in unison, if they are not familiar with the piece and are buried in their music, they do not stay together. There are many reasons why the RHYTHM is so important. First of all, keeping the BEAT is fundamental to staying together -- within a part, between the parts and with the accompaniment. Entrances and cut-off's and lengths of notes in the phrases all affect how the group stays together. We don't want anybody singing in their own time zone! RHYTHM defines where the consonants should line up. If the consonants do not line up, the DICTION becomes unintelligible. RHYTHM also affects the TEMPO. The conductor may start off at a fast clip, but unless the group stays with him, he has to relax the TEMPO to try to hold the piece together. And TEMPO affects the overall INTERPRETATION of the piece. When the TEMPO is off, the FEELING is off. And when the FEELING is off, so is the SUCCESS of the PERFORMANCE. Ultimately, we want to have a successful performance. So keep in mind how important keeping the RHYTHM is!
As important as learning the notes may be, keeping the rhythm together is even more important.