Know that from time to time a "tathagata" is born into the world, a fully enlightened one, blessed and worthy, abounding in wisdom and goodness, happy with the knowledge of the worlds, unsurpassed as a guide to erring mortals, a teacher of Gods and men. A blessed enlightened one. He proclaims the truth both in its letter and in its spirit, lovely in its origin, lovingly in its progress, lovingly in its consummation. A higher life doth he make known in all its purity and in its perfectness.
-Gautama the Buddha
The purpose of the avatar is to inaugurate a new world, a new dharma (teaching of the master). By his/her teaching and example they show how the human race can raise itself to a higher grade of life.
"Dharma" literally means mode of being. It is the essential nature of a being that determines its mode of behavior. So long as our conduct is in conformity with our essential nature, we are acting in the right way. "Adharma" is nonconformity to our nature.
The avatar helps us to return to our natural innocent angelic nature.
All of mankind should be the avatar or manifestation of God into the physical realm but it (mankind) falls short.
An avatar (AVATARA) is a divine being who has transcended the material realm and who does not have to be reborn into physical form again to finish its lessons, but who returns out of love and compassion for those lost and confused by creation, an avatar also come to update the spiritual message of eternal life using correct terminology for a more sophisticated human society. Jesus, who was called the Christ, was an "avatar."