Buddha Vajradhara is usually depicted naked when representing pure, formless voidness itself (dharmakaya). This particular images depicts the sambhogakaya, i.e. the form voidness takes on when it manifests symbolically to the extraordinary minds of highly-evolved Buddhist saints in their meditation. Each item of celestial raiments or ornament that it wears represents one or another quality of the buddha mind, such as total generosity, immaculate conduct and so on and so forth.
It is hard to put Buddha - the "indescribable" - into words. The closest that we can get is to study the chapters on buddha nature, enlightenment, buddha qualities and buddha activity in bodhisattva Maitreya's masterful work the mahayana uttara tantra, translated into English, with commentary, as "Maitreya on Buddha Nature" (Altea, Scotland 1999). This classic covers all the meaning of buddha nature taught in the final fifteen or so of the Buddha's discourses (sutra).
It is through their direct contact with sambhogakaya Buddha Vajradhara that the early Kagyu masters received the teachings that form the heart of our lineage.