The citizenship ceremony is a very important part of the process. First, at the ceremony you must make your pledge of allegiance. This is a legal requirement and you will not be an Australian citizen until you have done so.
You will not be able to apply for an Australian passport until you have attended a ceremony. If you do not attend a citizenship ceremony within 12 months of passing your test your application may be reviewed and cancelled. Exceptions may be made if you can provide justification as to why you have not taken your test, but you should not rely on this.
Secondly, you will receive your citizenship certificate at the ceremony. Your citizenship certificate is an important legal document, which you should look after. You will need it when you apply to get an Australian passport. It is an offence to deface or alter this document. You must not write on it, laminate it or change any details on it. You should notify the department if your certificate is lost or stolen.
Thirdly, the ceremony is an important occasion as it is a chance for you to celebrate your achievement with your friends and family.