Is the religion in Shingeki no Kyojin supposed to resemble a real-life religion?
Although I can't find a source stating this, I presume this might be based on the Jewish religion. In the Jewish religion there is the Kotel. This is a old wall located in Jerusalem which is used for prayer.  


  The Western Wall, Wailing Wall or Kotel is located in the Old City of Jerusalem at the foot of the western side of the Temple Mount. It is a remnant of the ancient wall that surrounded the Jewish Temple's courtyard, and is arguably the most sacred site recognized by the Jewish faith outside of the Temple Mount itself. source