The following below is a slightly amended version of my final answer to the Reality Sandwich interview of June 2014. Here it has been turned into a short treatise.
In the Name of God the Compassionate, the Merciful!
Praise be unto God, the Lord of the worlds, the Creator of all things, the Existentiater of all realities and all existences, Who, no other god is there besides It, is the One, the Single and the Unique! And blessings and salutations be upon Muḥammad and the Family of Muḥammad Who are the manifestations of the Logos-Self of Divinity and the Greatest Name!
Now then, when in the course of mystical wayfaring (sulūk) the faithful believer (mu’min) -- here meaning the gnostic initiate -- journeys within themselves from the temporality of the horizons of outer significance to that of the epoch of inner significances, they behold all existence as theophany and that every theophany reflects a form -- or Image, rather, the imago mundi -- to the intelligence of the heart which is its mirror and the locus of its manifestation.
Now, the Godhead in its utter remote transcendence and the absolute totality of Its infinitude cannot be known or represented by anything, because It is beyond all categories of predication or apprehension: ‘No vision perceives It, but It perceives all vision, for it is the Subtle, the All-Informed’ (Qur’ān 6:103). But the intelligence of the heart, what in Shiʿism is termed by the Imāms the ʿaql (Hiero-Intelligence/Nexal Consciousness), can through mystical wayfaring indeed come to know the form, the eternal Image, within the individuated mirror of itself as reflected by theophany, such that this knowledge (or noesis) becomes the knowledge and apprehension of its own self.
In Shiʿism the ultimate method to the attainment of this noesis is love (ḥubb) and its object is the Eternal Imām, which as hypostasis is also referred to as the Primal Will, the Pen, the Universal Intellect or the Muḥammadan Reality. The Eternal Imām is also interchangeable with the Fourteen Infallibles (i.e. Muḥammad, Fāṭima and the Twelve Imāms) (ع), whether individually or collectively. It is simultaneously both the supreme theophany of the Godhead as well as Its supreme veil, the Veil of Light, the Pleroma. Given this, a Shiʿi version of the Delphic maxim would hold that, ‘whosoever hath known their Self hath known their Imām Who is their Lord’.
That said, there is a famous Shiʿi version of a hadīth qudsī (an extra-Quranic saying of God) where God addresses the Prophet Muḥammad (ص), saying: “O Aḥmad [i.e. Muḥammad], were it not for you, I would not have created the universe; and were it not for ʿAlī, I would not have created you; and were it not for Fāṭima, I would not have created either of you!” If for the Shiʿi Muslim the mystery of the station of prophecy and messengerhood (nubuwwa/risāla) is embodied by Muḥammad (ص), who is the Seal of Prophets (khātim al-nabīyyīn/al-anbīya’), then the secret of this mystery is in the vicegerency or Providential Guidance (walāya) of ʿAlī (ع). Here both the mystery of the secret and the secret of the mystery are symbolically embodied by Fāṭima (ع) Who is proclaimed in this hadīth qudsī to be the existential raison d’etre of both, that is, the very purpose of the inner purpose to the most interior, animating intention of the creation of the universe: its supreme pivoting mystery, as it were.
Note that Fāṭima (ع) was once referred to by Her illustrious father (ص) as “the mother of her father” (umm abihā). Elsewhere in esoteric Shiʿism She has also been referred to as the Creatrix (al-fāṭir). As such, for a Shiʿi Muslim total devotion to Fāṭima (ع) as the Divine Mother represents the acme of faith and its consummation because here Fāṭima (ع) represents the Super-Celestial Earth of Divinity, the Earth of lāhūt (the pure divine realm). She is the Ocean of the Letter ṣād (ص) and the heavenly Lote-Tree beyond which there is no passing (ṣidratu’l-muntahā), the Tree of Life (shajara al-ḥayyāt), the Tree of Reality (shajara al-ḥaqīqa). She is the Radiant (al-zahrā’) because She is Light (nūr) itself and the Wisdom (ḥikma) incarnate. She is the Sabbath because she is the pre-eternal Day of the Cosmic Book (yawm al-kitāb).
Now, in another famous hadīth qudsī, God is held to say, “I was a Hidden Treasure and I desired to be known, therefore I created creation in order to be known.” The word for desire here in Arabic is ḥubb (حبّ) which also denotes love which as an attribute in Shiʿism is corresponded to walāya (the Providential Guidance). The ḥubb of the hidden Godhead manifests in the realm-worlds generated below the ipseity as the instantiation of the universal walāya (i.e. the Eternal Imām) that forms, as it were, the highest Pleroma. Here in the symbolism of the theophany of persons, Fāṭima (ع) stands as the ‘Hidden Treasure’, ʿAlī (ع) as the divinity’s ‘desire to be known’ and Muḥammad (ص) as the ‘creation of the world.” As such Fāṭima (ع) reflects the ipseity in Its modality of Exclusive Oneness (aḥadīya) and ʿAlī (ع) the Inclusive Unity (wāḥidīya) with Muḥammad (ص) reflecting the Unification (waḥdānīya). These are the three basic modalities through which the Divine Unicity (tawḥīd) can be spoken of.
Therefore, for a Shiʿi Muslim, to know and apprehend the supernal, divine reality of each via the intelligence of the heart, is to know what can be known of the Godhead in each of Its ascending and descending theophanies; and this, among other reasons too lengthy to explicate here, is what we have meant by the feminine Godhead in the context of esoteric Shiʿi Islam.
Furthermore, the Islam of Shiʿism is noetically completed within the intelligence of the heart of each believer only once the assent is made to the theophanic divinity of Fāṭima al-Zahrā (ع)’, which is an explicit assertion admitting to Her Providential Guidance (walāya), because at such a point when this assent is made by the intelligence of the heart, the ʿaql attains its own integral sophianity, its fāṭimīya, which is the level of the super-consciousness as exemplified by the Earth of lāhūt. Of course in all of this here we are speaking from the level of pure symbolism and pneumatology, and what these symbols mean to a Shiʿi gnostic in the process of mystical wayfaring as the Theophanies of the All-High reflect upon the intelligence of heart during the process of the integration of the Muḥammad-of-one’s-being, the ʿAlī-of-one’s-being and, finally, the Fāṭima-of-one’s-being who manifests to the soul the face of divinity, that is, the Supreme Horizon (ufuq al-aʿlā). And this here can also be taken as one of the countless meanings to the final theophanic sequence of the ḥadīth kumayl/al-ḥaqīqa, i.e. “extinguish the lamp for the Dawn hath indeed arisen!”
And God knows best, for no power and no strength is there save in God the High, the Mighty and the Supreme!
 مَنْ عَرَفَ نَفسْهِ فَقَدَ عَرَفَ إمامهِ الّذي هُوَ رَبّهِ
 يا أحمد لولاك لما خلقت الأفلاك، و لولا علي لما خلقتك، و لولا فاطمة لما خلقتكما
 کنتُ کنزاً مخفیاً فاحبتُ ان اُعرف فخلقتُ الخلق لکی اُعرف
 اطف السراج فقد طلع الصبح