Question: Why non-Muslims are not allowed in the city of Makkah?
Answer: It is true that only Muslims are allowed in the Sacred Mosque in Makkah. The simple reason it is so, is because it is the command God Almighty made in the Holy Qur'an.
Makkah and Madinah are cities of great importance in Islamic tradition- centers of pilgrimage and prayer, sacred places where Muslims are free from the distractions of daily life.
Restricting access to Makkah and Madinah is intended to provide a place of peace and refuge for Muslim believers and preserve the sanctity of the holy cities. Millions of Muslims visit the cities each year, and additional tourist traffic would simply add to the congestion and detract from the spirituality of the pilgrimage visit. These holy cities are not places of tourism, but places of reverence and worship.
A simple way to understand this better will be that there are rules and regulations for person wishing to enter a foreign country. He/she has to go through procedures like visa applications, passport, etc. No country will simply accept anyone and everyone. Why then should it not be such with sacred places like Makkah and Madina.
All citizens are not permitted to enter certain restricted areas like the cantonment. In every country there are certain areas where a common citizen of that country cannot enter. Only a citizen who is enrolled in the military or those who are connected with the defence of the country are allowed in the cantonment area. Similarly Islam is a Universal Religion for the entire world and for all human beings. The cantonment areas of Islam are the two holy cities of Makkah and Madinah. Here only those who believe in Islam and want to visit for pilgrimage and prayer are allowed. It would be illogical for a common citizen to object against the restriction on entering a cantonment area. Similarly it is not appropriate for non-Muslims to object against the restriction on non-Muslims against entering Makkah and Madinah. However, There are millions of mosques around the world, and if you wish, you are more than welcome to visit any one of them.
The Visa – The primary condition required for any human being to enter Makkah or Madina is to say with his/her Heart , Soul & lips, La ila ha illallah Muhammed ur Rasulullah meaning that 'there is no God but Allah and Muhammed (peace be upon him) is His Messenger'.
Sources: www.islamhelpline.com - islam.about.com - www.islamic-shield.com