Can Jews enter Mosques?
Responsum:It is permissible to enter a mosque, since most authorities have ruled that Islam is not idolatry.
The answer is more complicated regarding the question of entering a church, since authorities differ as to whether Christianity is idolatry or not. We can distinguish at least three opinions: the Rambam and those who follow him view Christianity as real idolatry; the Meiri denies any resemblance between Christianity and idolatry but views Christianity as a somewhat corrupted form of monotheism; some authorities say that Christianity is not idolatry for Christians, but it is for the Jews. This last opinion does not seem to make sense. If a certain form of worship is idolatry, it should be forbidden to non-Jews as well, since idolatry is one of the seven Noachide Laws. Thus we have to decide between the opinion of the Rambam and that of the Meiri. It seems that the disagreement between them stems from a difference in the definition of idolatry. The Rambam gives a philosophical definition of idolatry: idolatry is a misunderstanding of the essence of monotheism, and the belief in the Trinity is therefore idolatry. The Meiri, on the other hand, defines idolatry on the behavioural-ethical plane. Since the Christians in his day were lawabiding, he removed them from the status of idol worshipers. The deciding factor for the Meiri was not the way they think but the way they act.
This approach of Meiri has strong basis in the Torah. Many of the harsh laws against idol worshipers are accompanied by a description of their immoral behavior. In this disagreement between the Rambam and the Meiri, it is proper to follow in the footsteps of the Meiri, and his opinion is not unique, since many authorities ruled that Christianity is not idolatry.
In conclusion, it is permissible to visit mosques and churches. Before the visit, we recommend: visiting a number of synagogues; studying this responsum; studying liturgical texts of the three religious; teaching about the different goals of the different buildings.
The many authorities who permit entry into mosques do not differentiate between prayer times and other times. Since we have concluded that Christianity is not idolatry, it should also be permissible to enter a church during prayer. Notwithstanding this, the members of the Va’ad Halakhah are divided on this matter, and the answer also depends on the circumstances. For this reason, one should consult with a Masorti rabbi before the planned visit, and every case should be judged on its own merits.