These are multivalent terms, and so one has to be careful in their interpretation and in their use.  Basically they are philosophical terms that appear in various contexts that shades their meaning in one way or another.  For example, “dualities” appear in advanced mathematical analysis, and this yields some complex mathematical notions.  Also “dualism” is a common notion in psychology and in the science of human structure:  brain, mind….do these words refer to “2” separate entities or are they one and the same?  Is “mind” reducible to the biology and chemistry of the brain (nondualistic materialism), or is mind (and consciousness) something non-material that uses the brain like you use the computer.  Or, to put it even more radically, are you as a “person” reducible to the biology and chemistry of the body, or is there something more which we traditionally have called “the soul”?  This has been debated for a long time!  From Plato, the ultimate Western dualist, to many modern scientists who are “nondualists” in that matter is all there is, you can see that these terms can be applied in quite a few different contexts and with some very different consequences.  As far as science is concerned, I am definitely a dualist: there is more to reality than just matter.  But as regards spirituality, I am definitely on the nondualism side of the ledger.  And this is something I would like to explore a bit.  Nondualism itself has various shades of meaning, and perhaps different interpretations.  Many westerners are scared away from it because of that pop caricature of nondualism as a drop of rain vanishing in the “oneness” of the ocean.  Therefore they do not seek out any traces of nondualism within Christianity because…well, isn’t Christianity totally dualistic.  I suggest that this is a sadly and terribly wrong notion.

All the great religious traditions have their own approach to this matter, and interpret “dualism/nondualism” in their own particular way.  What you have to be careful about is skipping from the language of one tradition to another and thinking you are referring to the same reality in the same way.  It’s not that simple.  

Consider Hinduism.  It seems to cover all bases.  Whatever form of dualism/nondualism you want, it will provide!  The range of possibilities extends from a strict dualism that matches anything in the West; to a modified dualism (or modified nondualism if you wish), with its own treasure of bhakti, devotional practice that seems very close to Christian mysticism and the Sufis of Islam; to, finally, the total, radical nondualism of Advaita Vedanta, which in its turn comes in several types: from the austere mode of Shankara, to the complex tantric Kasmir Saivism.

Now Buddhism presents a different approach.  We are no longer concerned about relating to an Ultimate Reality.  The focus is on a kind of liberation from a “wrong view” of all reality, including our own self-understanding.  The liberation, or “enlightenment” is a kind of journey from living dualistically to a way of being that is truly nondualistic.  We awaken from this “dream” of seeing ourselves as this isolated individual self that stands in opposition to all other selves and the whole environment.  We discover an awareness of our intrinsic interrelatedness.  But here too there are variants, from Tibetan Buddhism to Chinese Zen to Theravada Buddhism and so on, each with its own nuances.

When we come to the great Western Traditions—Christianity, Islam, and Judaism—we encounter a very determined dualism.  Especially in Orthodox Judaism and orthodox Islam, the reality of God as the Wholly Other is emphatically asserted and all praxis revolves around that realization.  Christianity “softens” this dualism in the Mystery of the Incarnation, where the Wholly Otherness of the Divine enters the human reality.  Jesus is fully human and fully the Absolute Wholly Other we call God.  Traditional doctrine teaches this.  In itself it is a type of dualism, but what does that mean?   For sure this is not just a conceptual game of convenience to attribute two  fundamentally different terms to the same person.  These words refer to two different realities, not just concepts; but traditional doctrine also says that here we have reached the limits of what rational thought can do in grasping this Mystery.  True enough.  But we just slid by another very critical part of this doctrine:  Jesus is not some schizophrenic, “split personality;” not somebody divided up into two centers of consciousness; in other words he is ONE person, not two—this is traditional doctrine.  So the dualism of the “two” natures is transcended in the one person.  This points us in the right direction of discovering a very real Christian nondualism within a very dominant dualistic matrix of devotions, theology, self-understanding, living praxis, and ritual.  God is the reality you behold, you pray to, you obey, you seek, you worship, etc., etc.   Most believers never get past this awareness, but there is a deep mystical tradition within traditional, orthodox Christianity (as opposed to some off-beat variants that I am not referring to).  Christian mysticism has always been in a kind of tense relationship to traditional theology and authority.  On a conceptual level there is no way of reconciling these two tracks, but Christian mysticism simply uses the traditional language but pushes its meaning to a much deeper level, discovering its own form of nondualism;  and at the level of lived  religious experience there is simply no comparison.  Christian mysticism, then, does seem reasonably successful in finding its own nondualism while immersed in a totally dualistic religious paradigm.  The only other example of such that I can think of is the Sufi tradition within Islam.

But now I am thinking of Wordsworth’s poem, “Intimations of Immortality,” and I realize that what I am really looking for is not so much crumbs from the theological table that might suggest a form of nondualism, but more like the intimations of nondualism in the whole praxis of the faith, not just mysticism.  Like I said, the writings from the authentic mystical tradition of Christianity, both East and West, has a lot to offer to these “intimations of nondualism.”  Especially the Eastern tradition with its emphasis on “theosis” or divinization, participation in the Divine Life, rather than the Western emphasis on morality and “being saved from sin.”  But let us push ahead to what seems most common, at least in Catholicism, the practice of the celebration of the Eucharist, the Mass.  At first glance this practice looks like a true manifestation of the dualism of Christianity.  But look deeper this Lent.  There’s a reason Abhishiktananda was keen on celebrating the Eucharist even after his deep realization of Advaita!  Don’t get distracted or diverted by an approach to the Eucharist that I call “messaging.”  The celebration of the Eucharist becomes a series of messages.  Even worse is the “thinging” of the Eucharist, which in various ways turns the Eucharist into a thing which we “have.”  Now I do not mean to disparage anyone’s simple faith, practices, or understanding.  It’s just that wherever we are in our faith journey, whatever our state, we are always and everywhere at the gate of something infinitely deeper, and this is so true when we participate in the Eucharist.  But we do need to awaken to it.  Perhaps this is the real point of Lent, the true meaning of “conversion,” that awakening.   Once we realize that, we can freely participate in all traditional practices without anything limiting our vision; astonishingly enough, each practice is truly the “gateless gate” to our own version of Tat tvam asi.  Each practice is not for “gaining merit,” (there is nothing to gain really), not for “pleasing God,” or worshipping God, whatever that means, not for fulfilling an obligation, etc.; but each practice becomes simply a manifest, a theophany of the Divine Life.  It is the Christian “Namaste” to all of Reality.

Ponder also the simple words of the Gospel of John, which are also the most profound words written by any human being.  Yes, at first sight, the focus seems to be on Jesus Christ as the Other, the Wholly Different if you will, the object of our worship, etc.   But without negating any of this, we still need what the professional literary people call the “hermeneutical key” to reading  these simple but unfathomable words of the Gospel.  The hermeneutical key is the interpretive lens through which you understand the Gospel as a whole, and in the case of John you could almost miss this key because it comes to us in very common language:  door, gate, light, bread, way, etc.  You enter by a gate; you see by the light; you live by bread; you walk on a certain way.  (And ponder here Merton’s beautiful reflection on Jesus as the door in the Asian Journal.  It gives you a way to approach these words that uncovers the intimations of nondualism deep within them.)  

Here we begin to find Jesus not so much as the object of our attention, but as one through whom and in whom we exist and live and are connected to all that is Real (a Pauline thought also).  Now we begin to have true intimations of nondualism.  But the basic Christian focus on Jesus is not mistaken.  If you want to see what “living nondualism” is all about, just look at the life of Jesus, the person of Jesus and his teaching.  (Of course you might want to take account of the Semitic accent of the Gospel language; after all it is a language based in a certain cultural matrix.)  It is not some abstract theology or philosophy that is presented.  And from that contemplative gaze at the person of Jesus to our own “Tat tvam asi” THERE IS A BRIDGE, but I cannot tell you what it is because it is your own absolutely unique inner life manifesting the Divine Reality.   Something to ponder for Lent!