Arbaeen sign of emergence of son of man

And then shall appear sign of son of man in heaven :and then shall all the tribes of the earth mourn and they shall see the son of man coming in the clouds of heaven with power and great glory  Matthew Gosple chapter24 verse30

In thebible we can see clearly that say about a big mourn but what is it? Now ican answer you it is Arbaeen pligrimage that happen every year between karbala ans najaf( two city in Iraq)and alot of people frome all of the world or chrisyian or Muslim mourn for Imam Hussein (third imam of shia Muslim)