Enlightened mind, or Buddha nature, is the true nature of every being. Buddhists believe that all beings, not only humans, but also animals, including the tiniest insect, possess enlightened mind.
The true nature of the mind is enlightened, and it is peaceful and clear. The clear and peaceful nature of the mind can be understood both through our own daily lives and through Buddhist wisdom.
All of us can probably agree that if the mind is not disturbed by external events, emotional struggles, or conceptual rigidities, it becomes peaceful. The more peaceful our mind becomes, the clearer it gets. It is like water, which is peaceful and clear if it is not polluted or stirred. It is like the sky, which is pure and clear, if it is not polluted or covered by clouds. In the same way, when the mind is not disturbed by our rushing life and turbulent emotions, it is peaceful. The more peaceful it becomes, the more it gains in wisdom and clarity.
Emotions disturb not only our peace, but also the clarity of our minds. That is why we often hear people complain, “I was so angry I couldn’t figure out anything,” or “I was so upset, I couldn’t understand anything; I couldn’t see anything.” When overwhelmed by emotions or the speed of our busy lives, the mind becomes totally blind or blank, without much wisdom or ability.
Our mind’s natural state is peaceful and clear, and bringing it back toward this state is not only possible but important for improving our lives.
Buddhism goes even beyond this. Buddhists believe that the true nature of the mind, the actual mind itself, is enlightened. Enlightened mind is open, one, and omniscient.
Regarding the enlightened mind being open, when the enlightened mind sees things, it does not conceptualize in a dualistic manner. It sees everything as one in the natural awareness wisdom itself, like reflections appearing in a mirror.
If you do not use dualistic concepts, then you are totally open to the whole universe, like space, which is totally open, without any boundaries or restrictions.
We, however, are used to using dualistic concepts. When we see a table, we think, “That is a table,” and we see it there as an object. As we think of the table as an object, we position our mind as a subject, and duality is thus established.
Duality is followed by thoughts of discrimination—“This is a good table, a bad table, etc.”—and from there we build up a rigid world of walls and fences.
By contrast, the enlightened mind sees things in a total openness, without any condition. If there is total openness, there cannot be any boundaries, since there are no divisions of subject and object. Then, of course, everything is one, non-dual. If everything is one, there cannot be any conflicts or clashes, because conflicts and clashes exist only if there are two or more positions.
Now you must be thinking, “That means the enlightened mind is a sort of sleeping or blank state, because it does not even see objects.” No.
On the contrary, the enlightened mind is omniscient. The enlightened mind sees everything. Not only everything, but everything simultaneously. That is the quality of Buddha mind. In one sense the enlightened mind is so foreign to us it can be hard even to think about it.
However, we can get an inkling of it through stories of “near death experiences,” which I always love to quote. Of course some of these experiences can simply be hallucinations or induced by drugs. Yet on the whole, there are some amazing things revealed in these experiences.
Even people who have not necessarily realized the enlightened mind have some spiritual or inner experience during the process of death, before coming back to life.
According to what I have read in books and heard told, many people experienced traveling through a tunnel and meeting light at the other end. And as soon as they are touched by the light, they feel amazing bliss and peace. But the most amazing thing that they say is that bliss and peace are the light, and the light is bliss and peace. What they are feeling is light, and they are inseparable from the light. So these people are having an experience that is not channeled through the usual dualistic mind. Light is not just a tool to bring them peace. Light is the peace and they are the light, and so the subject, object, and the experience all are one.
Another man tells a story that for a few minutes after he died he saw everything that had happened in his life, from his birth till his death. But he did not simply see one event after another—he saw his entire life all at once. He was not really seeing with his eyes or knowing with his mind, but was just aware of everything vividly.
So, the enlightened mind is not really so foreign. We can all experience it when we realize the truth, or at some important juncture of life. But if you are not a meditator, you may not recognize the enlightened mind when you experience it and will be distracted again by the emotional and conceptual system of the world.
Source: Tulku Thondup. Edited by Harold Talbott. Enlightened Journey: Buddhist Practice as Daily Life. Boston and London: Shambhala Publications, 1995.

In Buddhism, the mind is the main focus—the source of all happiness and unhappiness, and the key to enlightenment.
We can improve ourselves only if we can discipline our minds.
If my mind is cruel, whatever I say will be words of harshness and whatever I do will be harmful to others and to myself, directly or indirectly.
But if I have compassion, gentleness, and wisdom in my mind and heart, then whatever I say will be words of peace, love, and joy, and whatever I do will serve and benefit others.
So, in order to serve others, we have to start with ourselves, and to improve ourselves we have to start with the mind, by disciplining it and developing Bodhichitta. And that is the essence of the Buddhist approach.
The next question is, “What is mind?” There are two aspects to the mind: enlightened mind and conceptual mind.
(Tulku Thondup. Enlightened Journey.)