وَأَنَّ الْمَسَاجِدَ لِلَّهِ فَلَا تَدْعُوا مَعَ اللَّهِ أَحَدًا

This verse establishes the fundamental principle that places of worship (masjids) are dedicated exclusively to Allah, and no one else should be invoked or worshipped in them. The word "masjid" literally means "place of prostration," referring to any place where people prostrate to Allah in prayer. The verse emphasizes the pure monotheistic nature of Islamic worship - in Allah's houses, only Allah should be called upon, prayed to, or worshipped. This prohibition extends to invoking saints, prophets, or any other beings alongside Allah. The verse teaches that maintaining the purity of worship spaces is essential for preserving the monotheistic foundation of Islam and preventing the corruption of faith through associating partners with Allah.