This is the question of Prophet Moosa (a.s.) to Allah when he was informed about Ashura.
And Allah’s reply to the question serves as a reminder about the importance of this Day in Islam and the reason why Shias in particular and Muslims in general organize activities like:
mourning ceremonies and assemblies (majalis) to revisit the grief of Aal Muhammad (a.s.),
elegy recitals (marsiyyah, nauha),
figurines (taaziyyah),
distribution of tabarrukaat, through which the mourners seek divine blessings
enlisting financial support for the aforementioned
Why Islam gained ascendancy over all nations?
Prophet Moosa (a.s.) asked Allah – O my Lord, how has the nation of Muhammad (s.a.w.a.) gained superiority over all nations?
Allah replied – I have given them excellence due to 10 characteristics.
Prophet Moosa (a.s.) – What are the 10 characteristics that they observe so that I may command the Bani Israel to likewise observe them?
Allah, the High, informed (about the characteristics):
Prayers
Zakaat
Fasting
Hajj
Jihad
Friday
Congregation
Quran
Knowledge
Ashura
Prophet Moosa (a.s.) said – O my Lord, what is Ashura?
Allah informed – It is
wailing or (in the least) pretending to wail or make one another wail and
grief over the son of al-Mustafa (s.a.w.a.)
and elegies and
mourning over the afflictions on the son of al-Mustafa (s.a.w.a.)
O Moosa, a servant from my servants in that era, will not wail or (in the least) pretend to wail or make one another wail and offer condolences over the son of al-Mustafa’s (s.a.w.a.) martyrdom but they will be settled in Paradise.
And a servant will not spend from his wealth a dirham in the love of the son of the Prophet’s daughter (s.a.) for food, etc. except that –
I will increase it in this world by 70 dirham and
he will be pardoned and
in Paradise and
I will forgive his sins.
And by My Honour and Majesty, a man or woman will not shed tears on the Day of Ashura or on another day to the extent of a single tear except that I will write for him the reward of a 100 martyrs.
Mustadrak al-Wasail v 10 p 318, Majma al-Bahrain p 403
After this tradition, Muslims in general should have a better idea about the importance of mourning and the place it occupies in Islam.
They should go all out to keep the mourning alive because without it, there is a question mark over their Islam.
In the least they should not raise baseless objections and lame excuses to stifle the mourning ceremonies especially if they entertain hopes of salvation and Paradise in the Hereafter, which as we have seen is reserved for those who observe mourning in and beyond Ashura.