The Islamic World shall Remain Indebted to Imam Husain (A.S.) until the Day of Resurrection.
"So when they (Abraham and Ismael) had both submitted their wills (to Allah), and he (Abraham) had laid him (Ismael) prostrate on his forehead (for sacrifice), We called out to him "O ham! "Thou hast already fulfilled the vision!" - thus indeed do We reward those who do right. For this was obviously a trial- And We ransomed him with a momentous sacrifice." Holy Quran, As-Saaffaat 37:103-107
In verse 107 the sacrifice with which Ismail was ransomed is described as momentous (extremely important or crucial, especially in its effect on the future course of events) by Allah, therefore it must be great in absolute degree. An ordinary ram by no means, in any sense whatsoever, can be termed as great; moreover, under no circumstances a ram can be greater than Ismail son of Ibrahim, both the most distinguished prophets of Allah, in whose progeny Allah had appointed Prophet Muhammad (p) and His divinely commissioned Imams. The ransom, therefore, is essentially a great sacrifice Allah had kept in store for future when the religion of Allah would be perfected and completed after the advent of the Holy Prophet (S.A.W.) and then it will need a great sacrifice to save its teaching from being destroyed by tyrannical kings of Banu-Ummiyah and Banu-Abbas.
It was indeed a great and momentous occasion when two men of God stood ready to offer to Allah that which was dearest to them to seek His pleasure, then Allah puts off this great manifestation of "devotion and surrender to His will" which was the real purpose of the trial (not blood and flesh) to a future date, so that the "devotion and surrender to Allah's will" should be demonstrated in a greater style and degree than what Ibrahim and Ismail could.
This great sacrifice was performed by Imam Hussain (a), grandson of last Prophet Muhammad (p), in 61 A.H. He was a descendant of Ibrahim (a) and Ismail (a), and according to Allah, son of Holy Prophet (p)(see Holy Quran chapter Aal-e-Imran 3:61, the verse of Mubahila). All Shia and most of Sunni authors of traditions and history have accepted the fact that "DHIBHIN AZIM" in Holy Quran refers to the sacrifice of Imam Husayn A.S., his family and his friends, peace be upon them all.
Imam al-Husayn (a) through his tragic martyrdom at Karbala revived Islam and preserved its authentic teachings from the hands of tyrants and despotic rulers. Hence, the Islamic world is indebted to this brave son of Holy Prophet Muhammad (p) and shall remain indebted to him till the Day of Resurrection.