Gambirangi is translation of the Upanishad and Shankaras commentary. Riddha manisha manasavhi krypto means in the heart. In the heart here means in the mind of the intellect. Sri Ramakrishna says should no manir gochar. It can be known by the purified mind. But what do you mean by the purifiedMind? Well that depends on the impurities.
Swami Sarvapriyananda teaches the Katha Upanishad, one of India's most revered texts which is also a part of the Vedas. It is a collection of philosophical poems representing a conversation between the sage Naciketas and Yama (god of death). They discuss the nature of Atman, Brahman and Moksha(liberation).