The Upanishads are, of course, among the great classics of mankind. The vast wealth of literature classed under this heading emerged from the spiritual golden age of India, a period during which the polytheistic and overly ritualistic religion of the Vedas was emerging into something simultaneously more spiritual and more philosophical. As with similar literature of a similar period from other places, such as Greece, the Upanishads often deal with the older literature in some novel ways, sometimes allegorizing upon it, often claiming to divulge a deeper meaning that has existed all along, and occasionally contradicting it.
When we zoom out a bit from the merely historical level, the Upanishads remain a fascinating example of the perennial nature of much mystical and philosophical thought. In this, they act as a demonstration of the universal accessibility of the truth at the heart of human life and existence. They are a reflection of the universal human condition and a testimony to the means by which man becomes master of that condition and, in a sense, transcends it. While their origins are in India, the Upanishads are part of the heritage of all mankind.
With this in mind, it must be admitted that it is a shame that the Upanishads have still not been fully explored by Christians in the discovery and appreciation of the “seeds of the Word” (as St. Justin Martyr termed the truths discovered and discussed by the pre-Christian philosophers). In this, the Upanishads contain a whole world of wisdom yet to be brought to its full fruition by exposure to and incorporation with the self-revelation of God in the Incarnation. I await the wonderful day this task will finally be taken up with the requisite erudition and sensitivity.
Juan Mascaro’s introduction is a bit too syncretistic to be realistic, but he certainly provides some decent pointers in the right direction toward understanding the Upanishads both on their own terms and in relation to Christendom. I think, however, that his style tries just a bit too hard to make the Upanishads as they are understood by modern Hindus fit in with Christianity in a way that is not possible if one is to allow both religious traditions to remain true to themselves. I recommend reading it nonetheless and extracting from it whatever is of worth to the reader. The Upanishads themselves I recommend for all readers interested in reading several of the great classics of spirituality.