Can someone explain this to me?

As my flair suggests, I am currently an Agnostic Christian, but I am thinking about becoming an Agnostic Atheist. But I want to learn more about *all* the current major religions to do that, so I can give unbiased advice and information to religious people! I started a quest today to read *all of* the religions' texts online, starting with the oldest religions to the youngest. So I started with Hinduism, and I started reading the Hindu texts with the Rig Veda. I decided to read the Rig Veda (and all other future religious texts) in chronological order instead of their traditional order, so I started reading with Mandala 6, as the Hindu writer Talegeri has stated that Mandala 6 of the Rig Veda is the first in chronological order. I have started the Rig Veda and have gotten through the first four hymns, and I have a question. Why is the god of fire, Agni, talked about so much so far, without introduction, if this mandala is the first in chronological order? And what important information should I know about him? Thanks in advance, Johnny.