Hajj refers to the set of prescribed routines you'll need to carry out in the holy land of Mecca. The Hajj pilgrimage is held in the month of Zulhijjah yearly. This can be also considered as an once-a-year collecting of entire world Muslims. Islam teaches that Allah has despatched messengers https://islamarticle.com/blogs/lessons-from-surah-al-kahf/