The great teacher Lama Yeshe once asked: “Why are there so many different deities in tantra?”  On one hand, Mahayana Buddhism speaks to universality, emptiness, oneness and the illusion of “I” or interdependent nature. On the other, Vajrayana Buddhism — often referred to as the “lightning path” and holding out the hope of realizations in one lifetime — includes the practice of deity yoga. These numerous deities appear contrary to the doctrine of emptiness/oneness — particularly from a Western cultural perspective.
Lama Yeshe answers this paradox: “Each deity arouses different feelings and activates different qualities … The whole point of doing meditation is to discover this fundamental principle of totality.” 
Although Vajrayana Buddhist practice begins on the universal Buddhist foundations of renunciation, refuge and contemplation, advanced practitioners are taught to visualize deities — and not just to imagine the deities, but to become them, merge with them or absorb them. Where foundation practices emphasize simplicity — notably, mindfulness meditation and contemplation of emptiness — Tantric Buddhism practices can seem overwhelming in the complexity of visualization and commitments.
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How does a modern Buddhist relate to this apparent contradiction? Western practitioners, in particular, can be quite put off by the apparent pantheon of deities.
One of my Buddhist friends asked, “Don’t all these deity practices foster superstition?” Which led to a long, spirited discussion—Buddhist debate being an honoured tradition—on what deity practice and visualization are really all about. Later, as I tried to explain to her the elegant concept of creation and completion stages, she said, “Then why bother creating what you’re going to dissolve into emptiness? Why not just accept emptiness?” My lame answer was something like, “Because it’s one thing to intellectualize the concept, another to engage in it. Otherwise, emptiness is just another label.” Hardly, a satisfactory answer, but the best a novice practitioner could offer at that time.
Sarah Harding, in Machik’s Complete Explanation, describes the underlying purpose much more eloquently:
“All visualized symbols, whatever other significance they hold are… understood as embodiments of the empty essence or primordial purity that is considered their true nature. Engagement with these symbols is aimed primarily at gaining access to this reality, which the practitioner learns to recognize as the actual substance of all symbols.” 
Loosening Preconceptions: Psyche and Soma
Rob Preece, a practising psychotherapist, explains it from a different, more Westernized perspective: “When we enter the world of Tantra, we may need to loosen some of our preconceptions about the nature of reality. We begin to inhabit a twilight world where the distinctions between the material and the symbolic are less defined. We discover that psyche and soma, the unconscious and matter, are in an interrelationship. The tantric view of reality does not make such solid differentiation between them; they are simply two reflections of the same ultimate nature. In the West, we habitually make a clear distinction between spirit and matter, whereas in the East these two are not separated.” 
Which brings me back to the great Lama Yeshe, who taught that once deity yoga is mastered, “The pure penetrative awareness cuts through relative obstacles and touches the deepest nature of human existence. At that moment of experience there is no conceptual labeling by the dualistic mind; at that moment there is no Buddha or God, no subject or object, no heaven or hell.” 
If the goal is to glimpse the “ultimate” and help use comprehend emptiness, why actually foster the practice of visualizing deities?
Rising Popularity of Deity Practice
Therefore, the question is, why is deity visualization rising in popularity in the modern, scientific age? One common answer, overly simplistic, is that the language of mind, and particularly subconscious, is a symbol. Deities are visualized (created) as symbols. In the language of Carl Jung, deity symbols are part of the “collective unconscious” of society.
Carl Jung, the great psychiatrist made extensive references to the powerful symbolism in Vajrayana, and religion generally: “Metaphysical assertions, however, are statements of the psyche, and are therefore psychological. … ” 
Jung summarized his own thoughts on universal symbols, subconscious and deities this way:
“We are so captivated by and entangled in our subjective consciousness that we have forgotten the age-old fact that God speaks chiefly through dreams and visions.” 
Stopping Ordinary Perception
A defining characteristic of Vajrayana and Tantra, and one of the many goals of Deity Yoga is “stopping ordinary perception.” Brian Hafer, Department of Religion Duke University, put it this way: “The Vajrayana school of Buddhism has been characterized as stopping perception… This is done by adopting a standpoint of having already achieved the goal and of one’s already being a Buddha as opposed to striving along the path towards enlightenment. Practices involving the adopting of the goal as the path are called Tantrayana, or the Effect Vehicle… The practices of Tantra are referred to as deity yoga because of the adoption of the viewpoint of having already achieved the goal (i.e. one’s already being a enlightened deity.)” 
Still, to scholars, or other Buddhists, Tibetan Buddhism might appear superstitious, especially given that “in Tibetan Buddhism, there is far more literature describing how to appease gods and demons, than there is on how to recognize them as nonexistent.”  Sarah Harding, introducing Machik’s Complete Explanation, clarifies:
“Are these two approaches contradictory, or meant for different elements of society: the ‘simple folk and the lamaist elite’ as David Neel calls them? I think not. Rather, these two approaches reflect the universal Buddhist instruction on dealing with all perception: to recognize it as inherently empty, and to apply skilful means…”
Deity yoga is not the only visualized method used to “stop ordinary perception.” Chod practice visualizes demons, spirits, and ghosts. “This is because all humans, each of us, must come to terms with the demons of fear, aggression, temptation, ignorance, and their cohorts if we are to live a free and sacred life, ” according to Jack Cornfield in his introduction to Tsultrim Allione’s Feeding Your Demons.  Where Chod “makes friends with your demons”, deity yoga asks you to “become the deity.” Both practices engage and stimulate Mind.
“Only in the Mind”?
It is easy to jump to the conclusion that deity visualization is strictly in the realm of dreams or “only in the mind.” In fact, another underlying purpose of deity visualization is to come to understand that “these two separate worlds… internal and external were one continuous seamless whole”  and that even mind itself is empty of inherent existence.
To help facilitate this understanding, a key goal of deity yoga is to cultivate bodhicitta, particularly “ultimate bodhicitta” that “perceives the emptiness (sunyata) of inherent existence of all phenomena.”  Emptiness is one of the most important teachings of Buddhism, and also one of the most difficult to understand. Deity visualization takes the practitioner beyond intellectualizing the concept of Emptiness.
“The deities of the Tantric Vehicle’s extensive pantheon, the male and female personifications of psychic processes as herukas and dakinis, are ‘produced’ by the yogi through the practice of controlled visualization until their reality overshadows that of the superficial apparent world,” according to the commentary in In Songs of Tibet’s Beloved Saint Milarepa. 
In fact, the yogi transforms not just the self to deity, but also the environment into the mandala (divine realm) of the deity. Divine pride develops as the visualization as deity becomes more and more vivid until it seems “real.”
The commentary continues: “When the reality of the apparent world has been overshadowed by the intensity of his realization, the yogi then enters the completion phase, where the illusory nature, or voidness, of his visualization, can be realized, and with it, the [emptiness] of the ordinary, apparent world. This is due to the fact that the apparent world is by nature an illusory ‘visualization’ derived from compulsive attachment to ingrained perceptions about the nature of things.”
The nineteenth century Tibetan guru Jamgon Kongtrul explained it this way:
“All phenomena of cyclic existence or transcendence, included within both appearance and mind, have no reality whatsoever and therefore arise in any way whatsoever.” 
The great Yogini Machik, the founder of Chod further clarifies: “When you realize that everything is mind, there is no object to be severed elsewhere. When you realize the mind itself as empty, severance and severer are nondual.” 
Other Benefits of Deity Practice
These lofty goals of Deity practice often overshadow the more mundane, but helpful benefits. “Visualizing yourself as a deity, as Tara or any deity, is very powerful. It’s a healing,” explained Venerable Zasep Tulku Rinpoche, the spiritual head of Gaden for the West, and Gaden Choling Toronto.  Zasep Rinpoche said, “we are the creators of our own suffering. Everything depends on our own mind.” 
The healing, from a Buddhist perspective, has to do with engaging the mind in purifying negativities. Or, put another way, putting cutting suffering at the source. It is the mind that forms attachments. It is at the level of mind we cut attachments that trap us in the endless cycle of suffering.
Venerable Lama Phunstok, during a White Tara empowerment, said: “All problems—sufferings, sicknesses, and diseases arise from thoughts that are based upon attachment, aversion, and ignorance as to the way things really are. It is said again and again that the worst obstacle is the third—concepts and thoughts. We continually think that we want to be happy and be free from suffering; we therefore never stop wanting more and more and as a result increase our attachment and aversion.”
Deity practice, in part, helps us to purify our minds by identifying with the perfect ideal of the enlightened mind. The health benefits are supported by a recent study from the National University of Singapore concluded that Vajrayana deity meditation significantly improves cognitive performance and health. The study concludes that even one session of Vajrayana deity visualization meditation brings immediate cognitive improvements. (See full story here>>)
A related technique, Chod visualization practice also has significant health benefits. “It is a well-known therapeutic technique. Chod certainly functions at this level where it can be very useful as a therapy. It is currently being taught… as a psychological technique for working with fear.” 
Deity is You, You Are Deity
Although deity yoga seems complicated, and it does require a teacher to benefit, it is also one of the easiest ways to explore and tame our own minds. The language of the mind, ultimately, at the higher levels of conceptualization, and at the deeper levels of the subconscious, expresses in the language of symbols, not labels. Deity yoga seems both profound and simple. In the words of Chokyi Nyima Rinpoche:
“The deity is you and you are the deity. You and the deity arise together. Since samaya and wisdom are nondual, there is no need to invite the deity… self emanated and self-empowered, Awareness itself is the Three Roots.” 
 The Bliss of Inner Fire: Heart Practices of the Six Yogas of Naropa, “Arising as a Divine Being” Lama Thubten Yeshe
- Publisher: Wisdom Publications (June 10, 2005)
- Publication Date: June 10, 2005
- Sold by:Simon and Schuster Digital Sales Inc
- Language: English
- ISBN-10: 086171136X
- ISBN-13: 978-0861711369
 The Psychology of Buddhist Tantra, Robert Preece
- Paperback: 276 pages
- Publisher: Snow Lion; 1 edition (November 8, 2006)
- Language: English
- ISBN-10: 1559392630
- ISBN-13: 978-1559392631
 Psyche and Symbol (1958), Carl Jung, p. 285
 The Symbolic Life (1953)
 Is Deity Yoga Buddhist? The Philosophical Foundations of Tantric Practice, by Brian T. Hafer, Duke University Department of Religion, Latin Honors Thesis, April 30, 1997.
 Drinking the Mountain Stream: Songs of Tibet’s Beloved Saint, Milarepa by Jetsun Milarepa. Wisdom Publications; Rev Sub edition (Feb. 8 2013) ISBN-10: 0861710630 ISBN-13: 978-0861710638
 Machik’s Complete Explanation: Clarifying the Meaning of Chod, Snow Lion; Expanded edition (May 14 2013)
- Language: English
- ISBN-10: 1559394145
- ISBN-13: 978-1559394147
-  Feeding Your Demons, Tsultrim Allione Little, Brown and Company; 1 edition (April 8 2008)
- Language: English
- ISBN-10: 9780316013130
- ISBN-13: 978-0316013130
 Venerable Zasep Tulku Rinpoche speaking during a 10 day Tara retreat in Nelson, B.C.
 Deity, Mantra and Wisdom: Development Stage Meditation in Tibetan Buddhist Tantra, by Jigme Linpa, Patrul Rinpoche and Getse Mahapandita. Snow Lion (May 11 2007)
- Language: English
- ISBN-10: 1559393009
- ISBN-13: 978-1559393003