Hajj, or the Pilgrimage to Mecca, is fourth basic 'Ibadat. It is obligatory only on those who can afford it and that too only once in a lifetime.
Mecca today stands at site of a small house that the Prophet Abraham (God's blessings be upon him) built for the worship of Allah. Allah rewarded him by calling it His own House and by making it the center towards which all must face when saying prayers. He also made it incumbent on those who can afford to visit is not merely to be a courtesy call. Even this pilgrimage its rites and conditions to be fulfilled which inculcate in us piety and goodness. When we undertake the pilgrimage, we are required to suppress our passions, refrain from bloodshed, and be pure in word and deed. God promises rewards for our sincerity and submissiveness.
The Pilgrimage is, in a way the biggest of all Ibadat. For unless a man really loves God, he would never undertake such a long journey all his near and dear ones behind him. Then this pilgrimage is unlike any other journey. Here his thoughts are concentrated on Allah, his very being vibrates with spirit of intense devotion. When he reaches the holy place, he finds the atmosphere laden with piety and godliness; he visits place which bear witness to the glory of Islam, and all this leaves an indelible impression on his mind, which he carries to his last breath.
Then there are as in other 'Ibadat many benefits that the Muslims can enjoy from this pilgrimage. Mecca is the center towards which the Muslims must converge once a year meet and discuss topics of common interest and in general create and refresh in then selves the faith that all Muslims are equal and deserve the love and sympathy of others irrespective of their geographical or cultural origin. Thus, the pilgrimage unites the Muslims of the world into one international fraternity.