Shankara says that the Atman should and can be realised only through knowledge and not by ritual. He asserts that on the dawn of knowledge, karma naturally and necessarily ceases to function. Karma of any kind is a hindrance to the final emancipation, and the performance of karma involves one in the cycle of samsara (the manifest, gross world). It is Brahmajnana that removes ignorance and bestows moksha.
Sannyas is absolutely necessary whether it be Vividisha Sannyas or Vidwat Sannyas. Without perfect renunciation it is impossible to pursue the path of Brahmajnana. The necessary qualifications are:
Without renouncing attachment to worldly life, knowledge of the Self cannot be pursued with vigour.
It does not mean that a sannyasin under values human society and discards all men without helping thorn. A sannyasin transcends the stages of spiritual evolution and at the same time exercises a silent and unnoticed but powerful influence for the good of humanity. Becoming one with the Devas in heaven is not the highest endeavour of mankind. There is something beyond karma, higher than the transitory earthly life, more transcendental than heavenly enjoyment. Even the Devas are subject to the misery of heavenly samsara and they are not immortal in the real sense. The Shrutis declare that Brahman alone is above samsara, above all experiences.
One who is intent upon realising the Peace, the Bliss, the One without a second - Shantam, Sivam, Advaitam - is the most powerful and useful friend of the world.