Why has Hezbollah joined the Middle East war?

Lebanon is once again drawn into a war many of its leaders say is not their fight. Against the government's warnings, Hezbollah has joined Iran in its conflict with Israel. The armed group says it has a right to respond as part of what it calls a resistance campaign. But this time, the Lebanese government has responded by taking the decision to ban Hezbollah's military activities and demanded it disarm. The group has not heeded that warning. Now, as the war between the U.S., Israel and Iran widens to Lebanon, can Hezbollah's involvement be of any real help to Tehran? And what price will Lebanon pay as a result?