The conquering of Mecca in 630 was a pivotal moment for Islam for several reasons, but primarily it solidified Islam as a faith backed by military support. This event demonstrated the political and military capabilities of the Muslim community under the leadership of the Prophet Muhammad, showcasing the transition of Islam from a persecuted group to a dominant religious and political power in the region.
The conquest allowed Muhammad to reclaim the Kaaba, which is the holiest site in Islam, and purify it of idols, thus reinforcing monotheism and the teachings of Islam. This act was significant in unifying the Arabian tribes under the banner of Islam, diminishing the influence of pre-existing pagan beliefs, and establishing Mecca as a central and sacred place for Muslim worship.
While some of the other responses consider aspects related to trade and relationships with other faiths, the central importance of the conquest lay in its affirmation of Islam's legitimacy and its establishment as a unified religious and political entity, which had lasting impacts on the subsequent expansion and spread of the faith.