The greatest teacher of the Vedanta philosophy was Sankaracharya. By solid reasoning he extracted from the Vedas the truths of Vedanta, and on them built up the wonderful system of Gyana that is taught in his commentaries.
He unified all the conflicting descriptions of Brahman and showed that there is only one infinite Reality. He showed that as man can only travel slowly on the upward road, all the varied presentations are needed to suit his varying capacity.
Shankara taught that three things were the great gifts of God :  human body  thirst after God and  a teacher who can show up the light. When these three great gifts are ours, we may know that our redemption is at hand. Only knowledge can free and save us but with knowledge must go virtue.
Books cannot teach God, but they can destroy ignorance; their action is negative. To hold to the books and at the same time open the way to freedom is Shankara’s great achievement.
…his whole life’s work is nothing but that, the throbbing of the beauty of the Vedas and the Upanishads.