Bergkirche contributes greatly to the religious and social life of this area. It's a nice place to enjoy a moment of prayer during a packed travel itinerary.
You're spoiled for sightseeing choice in Eisenstadt. Bergkirche is a great place to begin here, but there are many other fine spots to consider. Schloss Esterhazy, Esterházy Palace, and Haydn House are near the house of prayer and and will cap off your day nicely.