Upanishads deny any absolute form for Brahman
In the Kathopanishad we have this mantra:
न संदृशे तिष्ठति रूपमस्य न चक्षुषा पश्यति कश्चनैनम् । हृदा मनीषा मनसाऽभिक्लृप्तो य एतद्विदुरमृतास्ते भवन्ति ॥ 2.3.9 ॥
The bhashyam: कथं तर्हि तस्य अलिङ्गस्य दर्शनमुपपद्यत इति, उच्यते — न संदृशे संदर्शनविषये न तिष्ठति प्रत्यगात्मनः अस्य रूपम् । अतः न चक्षुषा सर्वेन्द्रियेण, चक्षुर्ग्रहणस्योपलक्षणार्थत्वात्, पश्यति नोपलभते कश्चन कश्चिदपि एनं प्रकृतमात्मानम् । कथं तर्हि तं पश्येदिति, उच्यते — हृदा हृत्स्थया बुद्ध्या, मनीषा मनसः सङ्कल्पादिरूपस्य ईष्टे नियन्तृत्वेनेति मनीट् तया मनीषा विकल्पवर्जितया बुद्ध्या । मनसा मननरूपेण सम्यग्दर्शनेन अभिक्लृप्तः अभिसमर्थितः अभिप्रकाशित इत्येतत् । आत्मा ज्ञातुं शक्य इति वाक्यशेषः । तमात्मानं ब्रह्म एतत् ये विदुः अमृताः ते भवन्ति ॥
The upanishad says that Brahman/Atman is not an object for ocular perception. It has no form. By extension, it is not an object of any perception, of touch, nose, sound and taste. These are specifically denied by another mantra of the upanishad:
अशब्दमस्पर्शमरूपमव्ययं तथारसं नित्यमगन्धवच्च यत् ।
अनाद्यनन्तं महतः परं ध्रुवं निचाय्य तं मृत्युमुखात्प्रमुच्यते ॥ १५ ॥ 1.3.15
The first cited mantra says,therefore, the way to know, realize, Brahman is only through the prepared mind, a subtle, pointed, intellect.
Shankara reasons that the form, space, sound, etc. are transformations of the elements and thus are not there in Brahman which transcends elements. Anything formed is finite and undergoes transformations and therefore perishable, as it is only owing to be created it can have any form.
It is only because of this, that all hold Brahman to be the object of the pramana called the veda, It being atīndriya. It Brahman had form, etc. then there would be no need for the veda, for it would be within the grasp of the sense organs.
There is a name ‘aprameya’ occurring in the Vishnu sahasra nama: 46. The word means: He who is not an object for any pramana. Shankaracharya’s commentary:
There is another name: anirdeśyavapuḥ 117. Shankara says:
Vishnu cannot be pointed out to anyone (by anyone) as ‘this is that’.
The Shvetashvataropanishat 4.20 too teaches that Brahman has no form, similar to the Kathopanishat seen above:
The Kathopanishat also teaches:
शरीरेषु अनवस्थेषु अवस्थितम्. महान्तं विभुमात्मानं मत्वा धीरो न शोचति ( Kathopanishat 1.2.22)
n the above we find that the Upanishad is categorical about Brahman not having a form. None can ‘see’ Brahman with the physical eye. One can however ‘know’ that it is Brahman that appears as the vishvarUpa. Again, one can know through the disciplined mind that Brahman which is without any form whatsoever.
However, as Shankara says in the BSB, Brahman/Ishwara can and does take on a form, any including the ones spoken of above, to bless/help an aspirant in his sadhana.:
स्यात्परमेश्वरस्यापि इच्छावशात् मायामयं रूपं साधकानुग्रहार्थम् । (1.1.vii.20) (Ishwara, out of compassion, takes on, by His Maya, a form to grace the spiritual aspirant.)
Thus, the true aspirant of Brahma jnana, who is also a true bhakta, as per Shankara, is quite well aware, on the basis of the Upanishads and yukti, that Brahman has no form and, therefore, no name as well. The primary logic here being that that which is not an object at all, but the very subject, cannot be a indriya grāhya vishaya. A name is given only to differentiate an object from all other objects. Since Brahman is no object at all, the question of its having an absolute name is also ruled out. This is the understanding of the Vedantic sadhaka.
Om Tat Sat