- To increase the volume of Imam’s recitation of the Holy Quran during the Paryers and the Khutbah (Lecture), because when this Qubbah became an usual part of Mosque architecture, there were no loudspeakers/microphones/amplifires etc. Muslims in those days rely on dome and
Mehrab technique to increase the voice volume.
- To create an identity that it is a Mosque and not any other building.
But keep in mind that Islamically, there are no specific outer architecturul requirements for Mosque structures. as such the design and outlook of Mosques varies throughout the Muslim world.
Minarates too are just to deliver the** Call for Prayer ** (adhaan) as far as possible.
Inside Mosque, no idols, no images are allowed. It has to be clean. Even shoes must be removed and kept outside the praying area.
Most mosques have ablution (Wudhu) area (where people take ablution before entering Mosque and praying).
Muslim architects out of their devotion, have created some unique characteristics of Mosque architecture. But all these are
Muslim and
not necessarily Islamic.
So keep in mind that Mosque architecture is a Muslim architecture and not an Islamic Architecture.
Islam and Muslim are two different terms.
Not everything that a Muslim does is necessarily an Islamic.