UPANISADS AND SIKH RELIGION
The Upanisads are considered the highest platform of evolution and philosophy of Hindu religion. The other Vedas are just considered elaboration and in event of any doubt Upanisads are final authority on all matters for Hindus. Upanishads exhaust themselves more simply knowing the true nature Self and who all qualified to follow various Paths and which Path leads to Self realization.
Looking at Isa Upanisad the first 14 paras describes the true nature of Self which conforms to rational belief of Formless attribute less etc God and in a way prohibits all forms of idol worship. How ever it very emphatically and clearly mentions throughout that the realization of self requires renunciation of world (three desires son, wealth and world) as Path to Knowledge (Vidya). For those who can not renounce can only have to live Path of Karma (Avidya) and can never be suitable for Path of Knowledge and realization of Self.
In subsequent paras from 15 to 18 it suddenly have changed context where it start advocating Sun and Fire worship. It has clear message of emphasizing rites not only for Karma but even for the Vidya.
The Sikhism has not much contradiction to concept of Formless, attribute less etc God. How ever as religion is path to achieve Self realization the Guru Nanak philosophy is to totally opposite to whatever is taught in Upanisads for Hindus. It says that the Path of Knowledge has to be pursued only along with Path of Karma and renunciation is strictly prohibited. It further criticizes all form of rites performed. These two philosophies of Life are as opposite to each other as Dialectics of Nature by Engel’s is to Hegel philosophy.
However the Sikhism philosophy in this way strongly recognizes the dignity of labour and in turn renounces the caste structure based more on division of labour and no labour than between types of labour. It however is not cynical in any way toward desire to acquire Knowledge as extremes some time in other western ideologies through undermining role of conscious. It simply contain their concern in Guru Nanak concept “Truth is Higher but Still Higher is Truthful Living”.