Prayer, fasting and zakat help us acquire religious competence and positively affect us from the social point of view. What about the Hajj? What is the logic behind the worship of Pilgrimage? What is aimed for people by obliging the Hajj?
First of all, the Pilgrimage is a command of Allah. We perform all the worships because He commands so.
Second: The month of pilgrimage is the midst of the three forbidden (haraam) months. In these months, nobody would harm another soul. A person would not touch the other, even if he saw the murderer of his father. Therefore, people would be safe, from the time they depart towards Mecca till they return home.
The following verses explain this reason:
“And announce the pilgrimage to humanity. They will come to you on foot, and on tired mounts. They will come from every distant point. That they may witness their benefits , and mention the name of Allah upon the cattle (an’am) He provided as sustenance, during the appointed days. Eat from it, and feed the unfortunate poor.” (Al-Hajj/ The Pilgrimage 22:27-28)
It used to be a world-wide market place. Everybody could meet in Mecca for trade and worship. Merchandising in Mecca carried on until Kharijite revolts. It was also a social environment for all the people on earth to coalesce.
Today, pilgrimage (Hajj or Umrah) is not organized the way it is prescribed in the Qur’an, but it should be.
 That they merchandise.