Hajj (Pilgrimage to Mecca) is one of the largest gatherings of human-beings on the face of Earth. Millions of Muslims respond in unison to this verse and others like it stated below.

"And complete the Hajj or ‘Umrah in the service of Allah" [TMQ 2:196]

Where hajj as obligation on every Muslim is a source to purify the sins, it has many consequences as well. The sins cannot be vanishing merely by performing haj, however, there are some worldly conditions that apply on it. One of them is the objective behind the Pilgrimage to Mecca i.e. the duty of Haji.

Haj or Pilgrimage to Mecca has collective spiriting in it which requires unity of Muslim i.e. the Muslim Brotherhood. If one do not deal with the other Muslim brother with good, the Hajj will be not be accepted by him/her.

The Muslims from all parts of the world who speak different languages and have different looks upon their faces all perform the various obligatory acts together like the Tawaf (Circuling) around the Ka'ba, the running between Safa and Marwa, the stoning of the Jamarat and the wearing of the Ihram.
 

Allah (SWT) said, “Verily the believers are a brotherhood”.

As the Prophet of Islam, Hazrat Muhammad (S.A.W) said, narrated by Abu Musa (R.A), "A believer to another believer is like a building whose different parts enforce each other." The Prophet then clasped his hands with the fingers interlaced (while saying that)." [Bukhari]

So after and during performing haj or Pilgrimage to Mecca, Muslims have to duty objective with them to treat with each other like brothers and not to fight with one another. If Pilgrimage to Mecca do not resulted that, the haj will not be accepted by Allah.

So who ever going to perform haj i.e. the haji, must not forget his/her duty i.e. the Muslim brotherhood.