Wāḥidiyya is the consideration of the Essence (dhāt) in terms of the diffusion of the Divine Names from Itself. The wāḥidiyya of the Essence with the Names is accompanied by the multiplicity of the Attributes. (Kāshānī, 47; Jāmiʿ, 103)
Aḥadiyya (absolute oneness) requires the absence of both the Names and Attributes, as well as their effects and domains of influence. Wāḥidiyya, on the other hand, necessitates the annihilation (fanāʾ) of the world through the manifestation of the Divine Names and Attributes, rubūbiyya (lordship) the subsistence (baqāʾ) of the world, and ulūhiyya (divinity) the annihilation of the world in the aspect of baqāʾ, and its subsistence in the aspect of fanāʾ. ʿIzza (Divine Majesty) requires the negation of the relationship between God and creation. Qayyūmiyya (Divine Self-Subsistence) demands the proper determination of the relationship (nisba) between Allah and His servant. For Qayyūm means the One who exists by His Essence, and whose existence is the basis for the existence of others; thus, it is inevitable that all the aforementioned requirements are fulfilled. Therefore, we say: from the perspective of the manifestation (tajallī) of aḥadiyya, neither Attribute nor Name is perceived. From the perspective of the manifestation of wāḥidiyya, creation does not exist, for it is an Attribute expressing the manifestation of His power in giving form to every being. From the perspective of the manifestation of rubūbiyya, both the Real (al-Ḥaqq) and creation (khalq) exist. This Attribute is necessary for the existence of both the Real and creation. From the perspective of the manifestation of ulūhiyya, only the Real exists. Yet, its wāḥidiyya form is creation, and only creation exists. Its inner meaning, however, is the Real. In the manifestation of ʿizza, the relationship (nisba) between the servant and Allah is abolished. From the perspective of qayyūmiyya, for the Attribute of Lord (Rabb) to exist, there must be an Essence to be accepted as Lord. Therefore, for the Attribute of Lord to exist, the Attributes belonging to the one who takes Him as Lord (marbūb) must also exist. (We say:) From the perspective of the Name al-Ẓāhir (the Manifest), He is the very reality of things. From the perspective of the Name al-Bāṭin (the Hidden), things are not His very reality. (Insān, 1, 12)
In aḥadiyya, the Essence manifests as Attribute, and the Attribute as Essence. In this respect, each of the Attributes is identical to the other. Just as al-Muntaqim (the Avenger) is identical to Allah, so too is al-Munʿim (the Bestower of Blessings) identical to al-Muntaqim. Again, when wāḥidiyya manifests both blessing and vengeance, the blessing, which is mercy, is identical to vengeance, which is punishment, and vengeance, which is punishment, is identical to blessing, which is mercy. Each of these is so in relation to the manifestation of the Essence in its Attributes and effects. Accordingly, if anything manifests for the Essence by the ruling of wāḥidiyya, everything there is identical. However, this is so only in terms of the manifestation of the One (tajallī-yi wāḥid). It is not so in terms of giving each rightful one their due; this latter occurs in the manifestation of the Essence (tajallī-yi dhātī). (Insān, I, 26)
The difference between aḥadiyya, wāḥidiyya, and ulūhiyya is as follows: In the Attribute of aḥadiyya, there is no manifestation of Names and Attributes; it is purely the Essence itself. In the Attribute of wāḥidiyya, there are manifestations of the Names and Attributes according to their spheres of influence. However, this manifestation occurs by the ruling of the Essence, not by a ruling separate from the Essence; thus, other existents are identical to one another. In the Attribute of ulūhiyya, the Names and Attributes manifest according to what they require, and thus opposites become apparent. For example, al-Munʿim is the opposite of al-Muntaqim, and vice versa. The other Names and Attributes manifest in the same way. For instance, aḥadiyya manifests in the Attribute of ulūhiyya according to the ruling required by aḥadiyya. Wāḥidiyya likewise manifests in the same way, for ulūhiyya encompasses the mode of manifestation of all. Each manifestation brings about what its ruling requires. For ulūhiyya is the station (maqām) of the manifestation of giving each rightful one their due.
The locus of manifestation for the saying, 'Only Allah exists; nothing exists with Him,' is aḥadiyya. The locus of manifestation for the saying, 'At this moment, He is as He is,' is wāḥidiyya. Everything other than His Essence will perish. It is thus necessary that aḥadiyya is superior to wāḥidiyya, for aḥadiyya is purely the Essence. Ulūhiyya, however, is superior to aḥadiyya, for ulūhiyya gives aḥadiyya its due, as ulūhiyya is the station of giving each rightful one their due. For this reason, ulūhiyya is the highest, most comprehensive, and most exalted of the Names. The superiority of ulūhiyya over aḥadiyya is like the superiority of the whole over the part. The superiority of the Attribute of aḥadiyya over other essential manifestations is like the superiority of the root over the branches. The superiority of the Attribute of wāḥidiyya over other manifestations is like the superiority of the whole over the part. (Insān, I, 27)
Then, the shaykh commands his murīd (disciple) to prefer retreat (khalwa) and seclusion (ʿuzla), and in this state to exert effort (gayret) to repel religious thoughts and the desires (nafsānī impulses) that preoccupy his qalb (heart), which cannot in any way be annihilated.
Know that a person at the beginning of the path of murīd-hood, while in retreat, is rarely protected from doubts regarding belief. Especially if the murīd possesses sharpness of qalb (heartly insight).