Why was a stick broken and placed on Queen Elizabeth's coffin?

A thin, white stick was broken by the senior-most official of the royal household and placed on Queen Elizabeth's coffin before it was lowered into the royal vault. The 'Wand of Office' is a ceremonial tool of the Lord Chamberlain, once used to 'discipline' people in the monarch's court. Its breaking signifies the end of his service to the monarch.