Any music, whether religious or secular, copyrighted or public domain, can be used in a religious service, without need of permission. That means you can use it however you want, including as an SATB arrangement. Obviously, if you can use the piece having to obtain permission, you may arrange it as you like.

Given that, it probably isn't a good idea to provide copies of the arrangement to anyone other than the people who will singer. For MichaelR, and others whose musical studies were neglected, SATB stands for Soprano/Alto/Tenor/Baritone.