Is it permissible for the Pope to pray in the Umayyad Mosque or even to enter it, and why?

It is permissible for a non-Muslim to enter a mosque out of necessity or for a benefit, such as inviting them to Islam, with the exception of the Grand Mosque (Masjid al-Haram). However, the leader of infidel Crusaders who fight Muslims and spread Christianization should not be allowed entry, as there is no benefit in their entering the mosque. Similarly, it is not permissible to allow a non-Muslim to practice their infidel rituals in the houses of Allah.