Om is the mantra of Kaal

Om is the mantra of Brahm (kaal). By reciting it, Brahm lok can be achieved. But one will not get peace and complete salvation by reciting Om mantra.

Shri krishna ji is other god than kaal God. By reciting Om nam, salvation can't be attained.

By reciting "Om" mantra of Brahm, one goes to brahmlok about which is mentioned in Gita chapter 16, that the worshippers who go to brahmlok also have rebirth.
It is stated that all loks including Brahmlok is perishable.

It is written in geetaji that salvation is possible only by right way of worship.
In the Gita Chapter 17, Verse 23 there is instruction of reciting Om, tat, Sat to attain supreme god. In this tat and Sat is symbolic. Only tatvadarshi saint knows these mantras. 

Saint Rampalji maharaj is tatvadarshi saint mentioned in geetaji. One can attain salvation by getting these mantras from him.

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