The most important command in Islam is Tawḥīd, which means believing in and worshiping Allāh (God) alone. This belief is the foundation of Islam, requiring that acts of devotion—such as prayer, trust, and gratitude—are directed only to Allāh, without associating any partners or intermediaries. It represents the pure monotheism that Islam teaches and is the central message delivered by all prophets.
The first command in the Qur’an highlights this principle:
“O mankind, worship your Lord, who created you and those before you, that you may become righteous.”
— Surah Al-Baqarah (2:21)