The dual nature of Buddha as one with the Absolute and at once actively pursuing the welfare of Beings, supplies the philosophical basis for the theological conception of the Trikaya of Buddha. They are namely the Dharmakaya, the Sambhogakaya and the Nirmanakaya. Vajrayana later added one more kaya namely the Mahasukhakaya to the existing trikaya system.
In Dharmakaya the Buddha realises his identity with the Absolute and His Unity with all beings. It is totally free of all duality and is the very nature of reality. Hence it is also called savabhavakaya. However, dharmakya is not the same as tathata since the latter is a metaphysical principle while the former is a person endowed with innumerable merits and powers. Dharmakaya has also been referred as Pure Will and as the Body of Essential Nature or the Vajrasattva. The Vajrasattva is the void, which is indivisible etc as well as the unity of the three centres of Body, Speech and Mind. Body, Speech and Mind are nothing but the transformation of the five components of phenomenal awareness. The Hevajra Tantra emphasises on the fact the dharmakaya is of the nature of Great Bliss and it is formless.
The Sambhogakaya is the splendour of the godhead which is concretely manifested to him and to the heavenly beings. The Buddha appears as Supreme God, abiding in the heaven surrounded by the Bodhisattvas
and other heavenly beings. He is endowed with thirty-two principal and eighty secondary marks of beauty and excellence. All glorifies accounts of Lord Buddha
in the scriptures reveal this body. It is with this body that he enjoys creation. According to the Hevajra Tantra the body has been acclaimed as a Body of Enjoyment which is known as the Mahasattva. It is the body resplendent with all auspicious signs and satiated by the flavours of the great blissful union which is the nature of creation and destruction. Unlike the dharmakaya, the Body of Enjoyment has a form and it belongs to the realm of samsara.
It is the apparitional body of Lord Buddha which saves being from misery. In the present time it is Buddha as Sakyamuni. Only to this body some form of historicity can be attributed. The Hevajra Tantra emphasises calls this body the Body of Creation or Samayasattva because it is the cause of the endless manifestations of Buddhas.
Mahasukhakaya is a Vajrayanic addition to the trikaya system of the Mahayana tradition. The kaya is the experience of the unity of three centres and is essentially nature of Bliss. Great Bliss is the secret instructions of the Boddhisattvas regarding the nature of things. This is considered the fourth body, the Body of Great Bliss.