Assalaam Alaikum Wa Rahmatullahi Wa Barakatuh,
Hajj is a universal congress for Muslim world.
For the blessed Hajj is worship at a universal level for everyone. Just as on a special day like a festival a soldier goes to the king’s celebrations like a General in the sphere of General, and receives his favours, in the same way, a Hajji, no matter how lowly, is turned towards his Sustainer under the title Mighty Sustainer of every region of the earth, like a saint who has traversed all the degrees. He is honoured with universal worship. For sure, the universal degrees of dominicality opened with the key of the Hajj, and the horizons of the tremendousness of Godhead which are visible to his eye through its telescope, and the spheres of worship which gradually unfold to his heart and imagination through its observances, and the heat, wonder, awe, and dread of dominicality caused by the levels of sublimity and last stage of manifestation, can only be quieted by “God is Most Great! God is Most Great!” (Allahu Akbar!), and those observed or imagined unfolded degrees can only be proclaimed by it. After the Hajj, this meaning is found in various exalted and universal degrees in the Festival (‘Eid) Prayers, the prayers for rain, and those recited at solar and lunar eclipses, and in prayers performed as a congregation. Thus, the importance of the marks and observances of Islam, also even if of the category of Sunna, lies in this reason.
From:
http://www.lightofquran.info/16word.htm