A teacher of seminary of Qom, Ayatollah Najm-al-Din Moraveji Tabasi in an interview said that during their times, Hazrat Fatima Zahra (AS), Hazrat Ali (AS) and Hazrat Imam Hassan Mujtaba (AS) explained the boundaries of the true religion of Islam, but the battle of Karbala and sacrifice of Hazrat Imam Hussain (AS) clearly defined the boundaries of religion of Islam to everyone.
He further said that the holy prophet Hazrat Muhammad (Peace be upon him) and Imams (AS) before Hazrat Imam Hussain (AS) mentioned the battle of Karbala. Imams (AS) after the battle of Karbala preached the message of Hazrat Imam Hussain (AS) and told everyone about the story of Karbala.
The main reason of emphasis on the pilgrimage towards the holy Shrine of Hazrat Imam Hussain (AS) was to connect the people with the aim of Hazrat Imam Hussain (AS).