Rock has an inherent problem when using it to send text messages, which is that you can have a person opted-in to receive SMS, but if they subsequently switch carriers and don't port their number, or cancel their service, that number will eventually get recycled and assigned to a new person completely unaffiliated with your church... and you're now sending texts to the new owner of the number... a person that never agreed to accept your SMS messages.
This is bad etiquette at best and possibly getting a complaint against you and/or having your messages marked as spam at worst. The solution is to implement the Twilio Deactivations API, which Rock could implement as a job that regularly (perhaps weekly?) downloads the list of deactivated numbers from Twilio and then inactivates any matching numbers in Rock. This would effectively prevent you from texting people that never agreed to receive them.
More can be read about the deactivations API here