What is the fundamental purpose of the Adhan (call to prayer)?

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The fundamental purpose of the Adhan is notification or proclamation. This is evidenced linguistically by the Almighty's statement: "And an announcement from Allah and His Messenger" (Quran 9:3), meaning notification. Similarly, in the verse, "I have announced to you on equal terms" (Quran 21:109), it means 'I have informed you,' establishing common knowledge. The prescribed Sharia Adhan is the established formulation recited at the times of prescribed prayers to announce their advent.