It is in the Bhagavad Gita that we come across the earliest and best exposition of the doctrine of the Bhagavata Sect. It extols the virtue of Karma Yoga through which alone human salvation is bellieved to be possible. It is the same work which lays the foundations of the avatara theory, the germs of which can be traced back even to the Vedic times.
The Avatara concept seems to be related to theory of cosmic evolution and is set forth in the idea of the birth of God among men again and again for the triumph of the good over evil.
Whether or not the modern inquiring mind appreciates the sentiments expressed herein, the fact that the entire earth was submerged in water millions of years ago should be accepted. Only very gradually the earth began to emerge out of the water.
1) It is but natural that the first incarnation was in the form of a fish, which can live only in water.
2) The next in order was in the form of a tortoise, which can live both in water and on land.
3) The third was in the form of a boar, essentially a land animal.
4) The fourth incarnation was a combination of human being and animal.
5) The fifth was in the form of a dwarf.
6) The sixth avatar was a regular man having an axe-like instrument useful to clear trees, etc.
7) The seventh was a man with a bow and arrow.
8) The eighth was a man with a plough as his instrument.
9) The ninth was Sri Krishna, the Supreme Teacher of the world.