The human tendency to exclusive concentration had an influence on the development of the later Upanishads. Having discovered and explicated the transcendent Absolute, the Brahman, the Upanishads began to focus exclusively on this realisation and left behind the offsetting and balancing impact of the equally important realisation that “all this is the Brahman.” This led more and more to an exclusive concentration on individual salvation through renunciation of the life of the world and the rise of Mayavada. The Veda and the earlier Upanishads recognised the universal creation and its importance, and treated the individual realisation as a step along the path of a divine victory for the universal. Sri Aurobindo reminds us of the need to circle back to this more balanced approach:
“Now certainly there is an emphasis in the Upanishads increasing steadily as time goes on into an over-emphasis, on the salvation of the individual, on his rejection of the lower cosmic life. This note increases in them as they become later in date, it swells afterwards into the rejection of all cosmic life whatever and that becomes finally in later Hinduism almost the one dominant and all-challenging cry. It does not exist in the earlier Vedic revelation where individual salvation is regarded as a means towards a great cosmic victory, the eventual conquest of heaven and earth by the supeconscient Truth and Bliss and those who have achieved the victory in the past are the conscious helpers of their yet battling posterity. … The Upanishad alone of extant scriptures gives us without veil or stinting, with plenitude and a noble catholicity the truth of the Brahman; its aid to humanity is therefore indispensable. Only, where anything essential is missing, we must go beyond the Upanishads to seek it, — as for instance when we add to its emphasis on divine knowledge the indispensable ardent emphasis of the later teachings upon divine love and the high emphasis of the Veda upon divine works.”
In his major work on yoga, The Synthesis of Yoga, Sri Aurobindo takes up the challenge he sets forth here by systematically reviewing and integrating the Yoga of Works, the Yoga of Knowledge, the Yoga of Divine Love and the Yoga of Self-Perfection.
Sri Aurobindo, The Upanishads, Kena Upanishad and analysis, pp. 187-188