The Holy Prophet (peace be upon him and his household) said: "Surely he is not Muslim who does not take interest in the affairs of Muslims. And surely he is not a Muslim who hears a Muslim calling for help and does not respond to his call"
The importance of Quds Day quoting from the Imam Khomeini’s speeches delivered for the same:
1- "Quds Day is the day when the superpowers should be warned to stay at home and leave the oppressed alone. Israel, the enemy of mankind, the enemy of humanity, which is creating disturbances every day and is attacking our brothers in south Lebanon, must realize that its masters are no longer accepted in the world and must retreat. They must give up their ambitious designs on Iran, their hands must be severed from all the Islamic countries and their agents in these countries must step down. Quds Day is the day for announcing such things, for announcing such things to the Satans who want to push the Islamic nations aside and bring the superpowers into the arena. Quds Day is the day to dash their hopes and warn them that those days are gone."
2- "Quds Day is the day when we shall discover which individuals and which regimes approve of the conspiracies of international groups and oppose Islam. Those who do not participate they oppose Islam and are in agreement with Israel, and those who participate they are committed, and in agreement with Islam opposing the enemies of Islam at the head America and Israel. It is a day when truth will be distinguished from falsehood, the day when truth and falsehood will be distinct."
3- "Quds Day is an Islamic day and a day for a general Islamic mobilization.
I hope that this event will be the precursor to the creation of a party for the oppressed throughout the world, which will go by the name of the party of the oppressed. I hope that all the oppressed will join this party to remove the obstacles that lie in their path; that they will rise up against the oppressors and plunderers of the East and West and no longer allow oppressors to tyrannize the weak of the earth; that they will make a reality Islam’s proclamation, Islam’s promise which is that the weak will rule over the oppressors and will inherit the earth."
4- "It is hoped that by keeping this day alive, indifference will be obliterated, negligence eliminated and the noble nations, through their uprising, will remove from the arena some of those perfidious leaders - who, despite the Muslims and Islam, hand in glove with Israel and following the command of America, continue with their shameful political lives and their criminal existence against the interests of the Muslims - and bury them in the graveyard of history."
* Source: shiachat.com