What does Vedanta mean in terms of the scriptures? Some regard Vedanta to be a continuation of the Vedas which it is if we consider Vedanta as being the focus on jnanakanda or knowledge in greater depth than can be determined from the Vedas.
The major source of scriptural material for Vedantic guidance have been the Upanishads. The central feature of the Upanishads is the saying that Aatman is Brahman (Atma is Sat-Chit-Ananda or ‘Reality-Consciousness-Bliss). This is mentioned in Mandukya Upanishad, second verse in ayam atma brahma; and in Chandogya Upanishad indicating the same in tat tvam asi, the rough translation being: ‘That Being which is this subtle essence, even That all this world has for its self. That is the true. That is the Atman. That thou art, O Shvetaketu.’ Then we have another major source of scriptural material in the Bhagavad Gita, which says something entirely different so that Vedantists have a dilemma on which course of understanding they are to proceed along and how to reconcile the two strands of scriptures. Of central importance is to consider what should be regarded as shruti.
Many attempts have been made to reconcile the two strands throughout the history of Hinduism and many traditions have developed. Essentially, however, the divergence is fundamental and unbridgeable. Vedanta via the Upanishads represent atheism whereas the Vedanta via the Gita represents the theistic submission. Both pathways can be described as advaitism, or oneness with Nature. In the atheistic version ancients were describing the religion that had no room for Sri Krishna as Paramatma by saying that ‘you are that’. This is the religion of Brahmanism given by the guna consciousness deity Brahma who inspired the Upanishads. On the other hand the Vedas and Gita were given by God in which the universe incorporated Sri Krishna as Paramatma and it generated the religion of sanatan dharma.
This brings the whole matter of what scriptures are to be regarded by Hindus as shruti into question. If shruti is defined to be the revelations of God for humanity, then only the Vedas and the Gita are to be regarded as shruti whereas the Upanishads must be removed. The Gita would then be seen as a special intervention by Sri Krishna to counter the threat to sanatan dharma posed by the Upanishads. It should be noted that the verna caste system is a central feature of this sanatan dharma. Advaita inspired by Brahma is a sattvic religion whereas sanatan dharma is neither sattvic, rajasic or tamasic but a blend of these gunas as the word of God.
Thus, the Vedanta for the followers of Sri Krishna is different from the Vedanta for followers of Brahma. The followers of Vedanta via the Upanishad tradition practice Brahmanism as advaitins or advaitists, whereas the followers of Vedanta via the Gita route practice sanatan dharma as devotees of Sri Krishna.
Either a Creator or Preserver God exists or it does not. Both are true only for agnostics (fuzzy wuzzy people who do not have much intelligence to make any decision) or atheotheists who are seekers who have not yet seen any evidence of God but have not ruled out that one day science will show him or her sufficient evidence as to constitute proof of God and so have yet to make up their minds. Adopting a religion or philosophy is however a different matter. By adoption one has already taken a position on this issue. Brahmanisim is atheistic and Sanatan dharma is theistic. So if you already subscribe to one or the other of these two religions you have to exclude the other.
In considering this issue, it is necessary to question: where in Vedic scripture does it say that Aatman is Brahman; and what is there in the Vedas that is consistent with or a repeat of ‘Tat tvam asi’? If there are no connection can advaita via the Upanishads can really be considered Vedanta?