Our consciousness is abiding at the moment as if we are living in a rented house. Soon we will have to leave this house to go to another house—we will get kicked out and the house will change. At the moment we have this shape, we are called a human being, and our consciousness abides in this body, or form. Then, after some time, the continuity of this consciousness migrates to another body, according to how we have lived our life every day, and according to those actions of body, speech and mind, done with good or bad motivation.
Sometimes there is a physical body and at other times there is no physical body. Sometimes there is only consciousness or the other aggregates, and no physical body. There are five aggregates, so even if there is no physical body, there are the other aggregates. However, there is always the continuity of consciousness, the labeled base and the aggregates.
This present life's continuity of consciousness continued from our past life. Just as the continuity of today's consciousness continued from yesterday, like that the continuity of consciousness has no beginning. As the labeled base, the continuity of consciousness has no beginning, so the "I" or the self, which is labeled on that continuity of consciousness also has no beginning. As it has no beginning, the continuity of consciousness also has no end.
If we don't change our mind and if we don't practice Dharma—if we don't eliminate the ignorance of true existence, the root of suffering and the creator of all the suffering that each of us experiences—if we always keep this in our heart and we do not change it, then endlessly, endlessly, our consciousness continues and we experience suffering in samsara endlessly. As the continuity of consciousness has no end, there is no time that it ceases and it always continues, so there is always the self. There is always the continuity of the self that is labeled on that continuity of consciousness. There is always continuity of the "I" that exists by labeling on that.
If we don't practice Dharma and if we don't do something with this mind—if we always remain under the control of delusion and karma and if we are always hallucinating about the ignorance of true existence—if we always live in this world, then we will endlessly experience the suffering of samsara.
If we change and practice Dharma, and if we eliminate the ignorance of true existence, then this continuity of consciousness attains the state of the omniscient mind, instead of continuously suffering and transmigrating to different samsaric bodies. The continuity of this present consciousness is able to approach the omniscient mind. This continuity of consciousness is able to become the omniscient mind, the holy mind of the Buddha, which is devoid of all mistakes and obscurations and is perfected in all realizations and understanding. When the continuity of this consciousness attains the omniscient mind, then the self which is labeled on that becomes the mind of a buddha. The mind becomes the omniscient mind and the self that exists on those aggregates, the "I" which is labeled on that, receives the name “buddha.”
We are now under the control of the unsubdued mind of ignorance and karma, and we are not free from that. So the self, the "I" that exists by labeling on that is a samsaric being, a suffering being, having obscurations. When this mind becomes the omniscient mind or when it approaches the state of omniscient mind, then the base is the continuity of this consciousness. The transcendental wisdom of the omniscient mind is the dharmakaya, and the absolute nature of that omniscient mind is called svabhavakaya.
The completely pure, omniscient mind is the continuity of this present consciousness. We could say it is just a way of talking about the future omniscient mind that we are going to achieve. The omniscient mind is the continuity of this present consciousness that is completely purified of all obscurations and is perfected in all the understanding. The absolute nature of that omniscient mind is also completely pure. So, the omniscient mind itself is the transcendental wisdom of dharmakaya, and the absolute nature of that is svabhavakaya, ngo wo nyi ku, or the state of self-nature. This translates as the holy body of the self-nature, but svabhavakaya is not a physical body, it is the state of self-nature.
Our mind, or consciousness, is not oneness with the obscurations. It is not oneness with ignorance, anger and attachment. Just as a mirror is not oneness with dirt, but is temporarily obscured by dirt, so our mind is stained by the obscurations but it is not oneness with them. It is temporarily obscured by veils such as the two kinds of obscurations, the more subtle obscurations to the omniscient mind [that block our enlightenment] and the more gross obscurations of delusions [that block our liberation].
Our present mind is temporarily obscured by these two veils, so it is not pure. Just as a mirror covered by dust is not clean, or just as a white cloth that is covered by the dirt of our body is not clean, like that our mind is not clean or pure. We can say that the absolute nature of the mind is pure because it is not oneness with the obscurations, however our present mind is not pure and stainless, because it is stained by obscurations. By practicing the remedy and by generating the path in our mind, we can remove the two obscurations and our mind becomes the omniscient mind, the transcendental wisdom of dharmakaya. The absolute nature of that becomes the svabhavakaya, the state of the self-nature, which is called enlightenment.
I think you heard a lot about these two terms—rang shin ney rig and gye gyur gyi rig. The first term is buddha nature or the clear light nature of mind. This buddha nature, or absolute nature of the mind, is rang shin ney rig. Then gye gyur gyi rig is the mind that causes enlightenment, and it is the continuity of this present mind that goes to enlightenment by practicing Dharma and following the path.