Guruji’s Words On Seva
G: One of the biggest benefits of seva is the washing away of negative karma. At the same time it gives further strength to the positive samskaras, which are helping your spiritual evolution. It works at both levels: increasing your positive samskaras and at the same time removing your negative samskaras. That is the energy of seva, of service.
As far as understanding what your seva is, the Guru energy will let you know through your heart.