Why are non-Muslims not allowed in the Holy cities of Makkah and Madinah?

It is true that non-Muslims are not allowed in the holy cities of Makkah and Madinah by law. The following points will serve to elucidate the possible reasoning behind such a restriction.

All Citizens Are Not Permitted in the Cantonment Area
I am a citizen of India. Yet, I am 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 are involved in the defence of Islam, i.e., the Muslims, 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 entering Makkah and Madinah.

Visa to Enter Makkah and Madinah
a. Whenever a person travels to a foreign country, he has to first apply for a visa, i.e., the permission to enter that country.
Every country has its own rules, regulations, and requirements for issuing a visa. Unless their criteria are satisfied, they will not issue a visa.

b. One of the countries that is very strict in issuing a visa is the United States of America, especially when issuing visas to citizens of the third world. They have several conditions and requirements to be fulfilled before they issue a visa.

c. When I visited Singapore, it was mentioned on their immigration form: “death to drug traffickers.” If I want to visit Singapore, I have to abide by the rules. I cannot say that the death penalty is a barbaric punishment. Only if I agree with their requirements and conditions will I be permitted to enter the country.

d. The Visa – The primary condition required for any human being to enter Makkah or Madinah is to say with his lips, “La ila ha illallah Muhammed ur Rasulullah,” meaning that ‘there is no God but Allah and Muhammed (pbuh) is His Messenger.’