The Glorious Qur'an says:
﴾And among you there should be some who invite to good, enjoin what is right, and forbid what is wrong, and it is they who shall be successful.﴿ (3:104)
Almighty Allah, the Lord of the Worlds, created humans only to worship Him and commanded them not to associate any being or anything with Him. Hence, from the early existence of humans, the Infallible Messengers (peace be upon them), that is, the Prophets (peace be upon them), were sent by Almighty Allah to guide humans and to protect them from the evil insinuations of their sworn enemy, Satan.
As we go through the Glorious Qur'an, we notice that from time to time, Prophets [to name a few: Adam, Noah, David, Abraham, Jesus ((peace be upon them)), and the last of them, Prophet Muhammad (peace be upon him and his household)] were sent for human guidance.
Before his death, each prophet appoints a successor by the command of Almighty Allah for the guidance of humans. Since Prophet Muhammad (peace be upon him and his household) appointed twelve Infallible successors for the guidance of humanity, the successors belong to the same "Divine Spirit".
The second beloved grandson of Prophet Muhammad (peace be upon him and his household), Imam Hussein (A.S.) was born on the 3rd of Sha'ban, in the year 4 A.H. (626 A.D.). He was brought up under the blessed guidance of his grandfather, Prophet Muhammad (peace be upon him and his household), and his father Imam Ali (A.S.).
After the martyrdom of his father and his brother Imam Hassan (A.S.), he initiated the divine mission for the guidance of humans.
Ten years after Imam Hussein's (A.S.) divine appointment, Yazid ibn Muawiya became the ruler. He distorted the teachings of the Prophet Muhammad (peace be upon him and his household) and of the Glorious Qur'an, openly legalizing all sorts of satanic actions in the name of Islam. He made lawful what was prohibited in Islam, e.g., consumption of alcohol, prostitution, bribery, slandering, lies, unveiling of women, etc.
Yazid was aware that the pious and faithful Muslims who were under the divine guidance of Imam Hussein (A.S.) will not allow his corrupt regime to survive. He ordered his officers to get Imam Hussein (A.S.) to pledge allegiance to him. Aware of Yazid's evil intentions, Imam Hussein (A.S.) refused the proposal.
On a divine mission to preach the Word of Allah, Imam Hussein (A.S.) was fully aware of the severe consequences of his action. Rather than considering Yazid's plea, he began his divine revolutionary movement to confront the forces of Yazid. His mission was to save the Glorious Qur'an, the teachings of the Noble Prophet (peace be upon him and his household), and to establish ethical values.
Imam Hussein (A.S.) was under constant pressure of Yazid's brutal army. On the 2nd of Muharram 61 A.H. (681 A.D.), he was surrounded by thousands of troops on the desert of Karbala in Iraq. Along with him were his blessed family and faithful companions, totaling 72 people. They fought the evil forces of Yazid very courageously.
Alas, on the 10th of Muharram, the divine Imam Hussein (A.S.), along with his blessed companions, were brutally massacred, thus attaining to martyrdom (shahadat).
In order to save Islam, Imam Hussein (A.S.) heroically confronted evil and did not surrender to the satanic Yazid.
The "message" we receive from Imam Hussein (A.S.) is to be always alert to evil and confront it, no matter what the cost.
We must follow our Lord of martyrs' teachings who practically demonstrated the blessed verses of the Qur'an:
﴾Enjoin what is right and forbid what is wrong.﴿ (3:104)
One of the great blessings granted by Almighty Allah after 1,400 years is the Islamic Revolution under the blessed leadership of the late Imam Khomeini (RA). Taking inspiration from the uprising of Imam Hussein (A.S.), the late Imam Khomeini (RA), in one of his blessed sayings, has said, "The survival of Islam is indebted to the uprising of Imam Hussein (A.S.) in the months of Muharram and Safar." (The Ashura Uprising in the Words and Massages of Imam Khomeini (RA), pp. 86,87)
Imam Hussein (A.S.) fighting evil is the symbol of the Islamic Revolution, for this Revolution also fought evil in the spirit of Imam Hussein (A.S.).