Transparancy.

Whenever there is a withering of the law and an uprising of lawlessness on all sides, then I manifest Myself.

For the salvation of the righteous and the destruction of such as do evil, for the firm establishing of the Law, I come to birth age after age.

- Bhagavad Gita, Book IV, Sutra 7, 8. 

The word "Avatar" is a Sanskrit word, meaning literally "coming down from far away." Ava (as prefix to verbs and verbal nouns) expresses the idea of "off, away, down." Avataram, (comparative) farther away. The root AV seems at all times to denote the idea of Protection from above, and is used in compounds, in words referring to protections by kings or rulers; in regard to the gods, it means accepted favorably when a sacrifice is offered. With the result that the root word can be said to mean "Coming down with the approval of the higher source from which it came and with benefit to the place at which it arrives." (From Monier-Williams Sanskrit Dictionary.)