Because the beginning of revelation is true dreams (ṣādiq ruʾyā).
The reason for this manifestation is the diffusion of light (nūr) to the maqām (spiritual station) of imagination (ḥayāl). As evidence for this, the following statement of Ḥadrat ʿĀʾisha is cited: To the Messenger of God (peace be upon him)... the beginning of revelation... that is, its manifestation... was through true dreams (ṣādiq ruʾyā). The Messenger of God’s (peace be upon him) dreams would emerge as clear as the morning light, that is, these dreams manifested in the realm of sensation (ḥiss). The statement is that of Ḥadrat ʿĀʾisha. She says, that is, Ḥadrat ʿĀʾisha, In the dream... that is, in the truthfulness of the dream... there is no concealment whatsoever. This is the tafsir (Qur'anic exegesis) of the Shaykh (Ibn ʿArabī) regarding Ḥadrat ʿĀʾisha’s narration. (Ḥadrat ʿĀʾisha’s) knowledge reached only this point, not beyond. (Sofyavi, 151)