Quote:
Mining is a distributed consensus system that is used to confirm waiting transactions by including them in the block chain. It enforces a chronological order in the block chain, protects the neutrality of the network, and allows different computers to agree on the state of the system. To be confirmed, transactions must be packed in a block that fits very strict cryptographic rules that will be verified by the network. These rules prevent previous blocks from being modified because doing so would invalidate all following blocks.
So the point of mining is to consolidate the records of bitcoin transfers in a way that the transaction record can't be tampered with. Miners are "paid" in bitcoin for performing that service to the community of bitcoin users.