Atarium means this reality, our own nature, is not subject to reasoning. And shankaracharia here commences, nahi kutarkaso nista quatit vidate. Just by argumentation, just by reasoning, you will never come to a firm conclusion. So why not go straight to the openishads and use the pointers and become enlightened? It won't work. They have to be skilfully employed by a person who has actually realized that i am brahman. In the hands of that person, these texts can serve as powerful pointers and help us to realize our real nature.