In the overall scheme of things, the creation is designed to be self-maintaining, self-sustaining, and self-correcting. The universe is meant to exist. Yet it can only continue to exist if there is harmony. When the abuse of freewill creates disharmony, the potential of the self-correcting mechanism throws up a force to restore the harmony. This is how the avatara or incarnations are described in the scriptures. We also observe that this happens from time to time. It may be difficult for us to determine whether or not a given manifestation is an avatara, but we can understand the principle behind it.
Swami Viditatmananda Saraswati
Excerpts from Satasanga with Swami Viditatmananda Saraswati Vol. 1