The following quote is a commentary on the nature of God by a major Shi’ah thinker, Imam Jafar as-Sadiq (AS), who is also considered an important mystical figure. Moses (AS) is a major figure in the Muslim tradition, and symbolically is used to reference legalism and law. His interaction with the Divine helps to establish our understanding of God.
As far as we can tell, the first major development of the concept of divine speech was the work of the sixth imam of the Shi`ah, Ja`far al-Sadiq (d. 148/765). Respected for his piety and wisdom by all Islamic sects, Ja`far was regarded especially highly by the Sufis, who took his Qur’an commentary as the basis for their growing body of mystical Qur’anic literature. In his exegesis of the theophany experienced by Moses on Mt. Sinai, Ja`far found the key to the nature of divine speech in the words by which God identified Himself. According to Ja`far, when God said to Moses, “I am I, your Lord (inni ana rabbuka)” (Qur. 20.12), Moses then realized that
it is not proper for anyone but God to speak of himself using these words inni ana, “I am I.” I was seized by stupor (dahsh), and annihilation (fana’) took place. I said then: “You! You are He who is and who will be eternally, and Moses has no place with Your nor the audacity to speak, unless You let him subsist by your subsistence (baqa’) and You endow him with Your attribute.”… He replied to me: “None but I can bear My speech, none can give me a reply; I am He who speaks and He who is spoken to, and you are a phantom (shabah) between the two, in which speech (khitab) takes place.”
Quoted in Ernst, Carl W. Words of Ecstasy in Sufism. SUNY Series in Islam. Albany: State University of New York Press, 1985, pg. 10.