Ishvara is not something we can prove through logic, if this was possible, all mathematicians would be jivanmuktas. It's only in the deepest stages of samadhi that our ancient rishis were able to percieve the ultimate reality and record the vedas. Swami Dayananda and his arya crowd are what I would call "pseudo-rationalists." A lot of Swami Dayananda's translations of the vedas have been discredited by scholars, for example in the karapatra bhashya a lot of Dayananda's inconsistencies have been shown.
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