about service tax

why service tax is collected and why it is remitted to the government ? suppose a client comes to file his return of income. the chartered accountant will render his services and he will help the client to return his file of  income . now the chartered accountant prepare a bill on the client and he prepares with the addition of service tax . suppose ca charge him 600 rs + service tax . then why service tax is collected from the client and remitted to the government . the services have been rendered by the chartered accountant that is why he is collecting that above mentioned 600 rs but why with that service tax is included .............? wat is the connection of service tax and remittance to the government .