The martyrdom of Imam Husain (AS) gave the Muslim Ummah the biggest shock which saved the Ummah from collapse when the rulers (Yazeed and his gangsters) were totally away from the teachings of Islam. Muslim masses could not accept the crime of the killing of the grand son of the Prophet along with his family members including children and imprisonment of the family of the Prophet (SAWA). This greatest shock brought back the sense to the Ummah and was the reason behind hundreds of revolts against tyrant rulers during centuries of the history of Muslims. Imam Husain's martyrdom declared the tyrant rulers as deviants and made the Muslim masses careful when dealing with them.
The martyrdom of Imam Husain (AS) became the guide to his noble value which calls Muslims to be real Muslims and join good and avoid evil. Thousands of scholars, writers, poets were inspired by Imam Husain's martyrdom.
Millions of Muslims all over the world and all over the generations, observe the martyrdom of Imam Husain every year and get spiritually charged to be better Muslims.
Imam Husain's martyrdom has inspired many non Muslims and made them realize the great teachings of justice for which Imam Husain (AS) has sacrificed.
The list of the benefits from Imam Husain' martyrdom will be very long and books can be written on it, but to cut it very short, we need to remember the Prophetic Hadeeth which stated: Husian is from me, and I am from Husain. How the grand father is from his grand son? In fact, he religion of Islam which was sent through the Prophe Muhammad (SAWA), was revived and made everlasting because of Imam Husain (AS).
Reviving Islam is the great benefit not only for all Muslims but for all mankind.