“Yi” means the mind, and “dam” means samaya which is our connection or relationship. So “yidam” means the karmic connection to wisdom or one’s connection to wisdom. Yidams are our connection to the wisdom of enlightenment. They are not worldly beings but enlightened beings. Most protectors are still in samsara, but yidams are not in samsara.
Tibetan families and lineages often have a personal specific yidam, or connection to wisdom. This can be the main connection that a family practices together and passes down through their children.
"Tantric practitioners find that devotion to the deities leads to the recognition that their deeper selves are the deities. In guru yoga, the student must find the mind of the master within."
~ Tenzin Wangal Rinpoche's Healing with Form, Energy and Light
Yidam deities are not external to one’s own mind, rather they are images that help us work with our own mind. Yidams are the unblemished reflection of the primordial and innate true nature of our mind that manifests in specific forms and colors. The purpose and goal of our practice is to attain perfect Buddhahood, which manifests in three aspects or forms at fruition – the Dharmakaya, Sambhogakaya, and Nirmanakaya. It is important to know that the three kayas are indivisible.
Meditating again and again that one’s body, speech, and mind are not different than the pure body, speech, and mind of a Yidam and that they are indivisible decreases and eventually eradicates one’s attachment to the ordinary idea one has of oneself that one clings to and that one is convinced really exists. It happens naturally and isn’t hard identifying with one’s ordinary body, speech, and mind and calling it “me,” and it isn’t easy giving up clinging to the impure body, speech, and mind one identifies with so strongly and points to as “I.” One needs to exert energy and practice, seeing one isn’t accustomed to experiencing the true and pure nature of one’s being. The aim of generation stage tantra is to progressively replace one’s ordinary, gross perception with a pure perception of what is true.
Internal visualization of a yidam means you are training your mind. You are transforming the mind, our palace of five wisdoms. Where is this palace of five wisdoms? In the center of our heart. It is this mind that abides in the center of your heart that transforms into the yidam. At that time, don’t feel that the yidam is just in the heart and the rest of your body is still your ordinary physical body. That is not the visualization. When it says “your mind transforms into the yidam” that means that you transform into the yidam. When you transform into the yidam, this means all of your connections, your body, your speech, your thoughts, your contaminated phenomena, all of that you call “I” transforms into the space of the luminous yidam. At that time you are in the state of the yidam.
But what does it mean to be in the state of the yidam? The yidam is said to have many symbolisms such as three eyes, one face, and two hands but all of those are symbols not reality. Symbolisms are not real. We utilize symbolism to help us understand. If we were to say the yidam is just space or just emptiness, we might not understand. Thus we use symbolism to help us understand. The main reality of the yidam is your own mind – the nature state of your mind. You need to connect with that state. If you transform that state into the symbolism of the yidam that is enough. If not, then just connect with that nature state of mind. When you are connected with the nature state of mind you are transformed into the yidam. This is the deeper meaning of the internal visualization. Mind itself connects with it’s own self-knowing awareness.
Also it's important to note that we typically use the word "visualize" when we talk about yidam practice, but it's merely a translation. Often we may think "to visualize" as using only our sight or seeing. But that is not what is meant by visualization in the practice. A better translation might be "feelization."
It is this feelization which is this notion of re-inhabiting or re-living an emotional experience is this practice and meaning of visualization. Visualization in this tantric sense of the word can be visual imagery. But there is so much more that comes with it. Bodily felt and held experiences, emotions, narratives, etc.
An example of visualizing that we may habitually do is with unwholesome mind states. We don't just intellectually remember it like "How interesting that someone wronged me back then." but instead we re-inhabit the emotion. We re-live the memory through emotionality. And we do this again and again. An example of this is holding grudges, where we re-inhabit the memory. And we know how to do this very well. Another example is lust. We don't just intellectually recall lust, but re-inhabit and re-live it again and again. Both with anger and intense attachment. Perhaps you can recognize being in these alive states of re-lived emotionality?
And so this tantric practice of visualization is to invoke this re-inhabiting or re-living of emotional experiences but instead of the emotional experiences of the five poisons which we do so well we re-inhabit the qualities of our buddha nature. We use this same process that keeps unwholesomeness alive in us, to generate and keep alive all the wholesome qualities that are and always have been present in our original nature.
Is the Yidam deity we meditate a truly existent, permanent entity?
It is important to know that this is not the case. All Yidams arise in dependence in that they are created by our own mind. If one meditates a Yidam deity that one creates and cultivates with one’s mind intensively for a long period of time and accomplishes the aim of the practice, then one will have realized the actual and true manifestation of the Sambhogakaya.
The main purpose of practice is to transform one’s impure perception of appearances and apprehension of experiences that determine one’s life into pure and untainted perceptions and apprehensions. Therefore, in order to cleanse one’s impure way of perceiving and apprehending things, one repeatedly meditates the immaculate appearance of a Yidam deity. Practice consists of focusing one’s attention on a pure image of enlightenment, a Yidam, until one’s perception of the purity of all appearances becomes clear and brilliant and determines one’s life. It isn’t possible to attain this goal right away, and that is why beginners fabricate thoughts about a Yidam while cultivating it during meditation practice.
Practitioners can have doubts and wonder whether the Yidam exists or not and whether the practice is beneficial or not. There is no reason to have doubts if one is aware of the fact that the image of the Yidam is not born outside oneself, since one knows that one is creating it with one’s imagination and with one’s eyes closed. If one continues practicing, then eventually one will see the image of the pure deity as the manifestation of one’s own perception with opened eyes. It’s important to be assured that a practitioner doesn’t walk around seeing blue or white images holding flowers in their hands, rather fruition means that a successful practitioner sees phenomena free from any personal, conceptual and emotional blemishes.
Certain texts especially in the Tengyur are written in twilight speech so that since the Tengyur is available for anyone who's literate to read you can't do them without the oral instructions or the ability to decipher twilight speech.
Twilight speech is in symbols. So if twilight speech tells you "to put your dorje in a white lotus blossom" do not go get the dorje on your altar and go find a lily pad with a blooming lotus and stick the dorje in the lotus. It's talking about consort practice.
When you do ngondro you learn a lot of the patterns in twilight speech. It's one of the benefits. If you do the full set of ordinary and extraordinary ngondro you will have learned about half to three quarters of the symbolism used in twilight speech. So that you know what the "horns of a rabbit" is or the "hair of a tortoise." If you are instructed to go get some and mix it with some other substances you will understand what that text is actually telling you to do rather than run around all over the world trying to get very difficult to acquire substances. They symbolize either certain tsa lung activities or certain meditative activities. That's twilight speech.