[James]

I don't understand what he is trying to achieve Brexit-wise calling for a new election.

Labour's position on Brexit at the last election (no single-market, no actual customs union, an end to freedom-of movement) would have just resulted in a pretty-similar deal to the one that was just rejected. As far as I can tell the policy hasn't changed.

Any party getting a large majority is very unlikely.

He just wants an election to fulfill his ambition to be Prime Minister, and do all the other things he wants to do. It's not going to sort out Brexit in anyway.