An audio interface can be a very useful piece of tech equipment for worship ministry leaders - even those who are working in a traditional or classical style. What does an audio interface do? It connects your microphones and other sound sources to your computer, bridging the gap from analog to digital. This means that you could record your choir or band performing at a remote location or practicing in a rehearsal room that doesn't have built in A/V equipment, and all you would need to bring with you is your laptop, a few microphones, and an audio interface. Audio interfaces range in price from under $100 for a simple unit with a limited number of inputs, up to several thousand dollars for complex interfaces with more than a dozen inputs. Some are portable while others are built to be mounted in an equipment rack.
With so many choices, confusing terminology, and various use cases, a detailed buyer's guide is invaluable. The guide provided by Musician's Friend is a good place to start.
And, while not the right choice for everyone, I've found my MOTU Audio Express to be a great balance of power and portability.