In order to make primordial simultaneously arising clear light mind fully and completely manifest, we must totally stop or cease all coarser levels of energy-wind and mind. In order to stop the coarser levels of energy-wind and mind from predominating, we need to generate a greatly blissful deep awareness. To generate a blissful awareness that is sufficiently intense and powerful to accomplish these aims, it is necessary for most persons to rely on a mudra, a sealing physical partner. The reason why the central Buddha-forms in the mandalas or symbolic universes of the anuttarayoga tantra class are mostly in the aspect of a father and mother couple is to indicate this necessity. There is a great difference between relying on a sealing partner with full awareness that doing so is solely to provide the circumstance and source for developing a greatly blissful awareness to be used for the above purposes, and relying on one as a pathway of practice in the manner of a trespasser. Therefore, only especially well-qualified practitioners well-advanced on anuttarayoga tantra's complete stage who have trained in the practices of the subtle energy-channels and winds and who have gained mastery over them, are permitted to practice with an actual, physical karmamudra, a sealing partner for their behavior. Because they have gained full mastery over their energy-winds and channels, such practitioners never have the danger of experiencing the ordinary bliss of orgasmic emission [orgasm] that would either prevent or destroy their generation of a greatly blissful deep awareness. They are merely using their external and vajra-bodies as a mechanical device to intensify the blissful awareness of voidness they have already achieved.
Before we have reached this advanced level of accomplishment, we are permitted to practice only with a visualized jnanamudra, a sealing partner for deep awareness. In An Ornament for "The Stainless Light" [Commentary on "The Abbreviated Kalachakra Tantra"] Kgiydrub Norzang-gyatso has explained that, for practitioners of especially sharp faculties, relying on a visualized jnanamudra partner can also serve as a method for generating a greatly blissful awareness strong enough to dissolve at the center of the heart chakra all the energy-winds that are the most difficult to dissolve so that the clear light mind becomes totally and completely manifest. Thus it is not absolutely mandatory to rely on a physical karmamudra partner.
But regardless of our level of realization, and whether we are practicing with a visualized jnanamudra partner or a physical karmamudra one, it is extremely essential to keep the purpose in mind and never practice without the three types of discernment or recognition. In order to block the mind's ordinary appearance-making and apprehension of true and inherent existence, we visualize ourselves and our partner in the aspect of Buddha-forms made to appear by a mind that is blissfully aware of voidness. We discern our speech as the expression of clear light mind of inseparable bliss and voidness, symbolized by the seed syllables from which the appearance of our sexual organs arises in a purified form and with which they are "crowned" or marked. Furthermore, we understand our mind as always being a primordial clear light mind that arises simultaneously with each moment as a blissful awareness that is inseparable from also being a discriminating awareness of voidness. These are extremely important points that render reliance on a visualized or physical sealing partner into a skillful method on the path. Such reliance generates a deeply blissful awareness that acts as a circumstance for blocking the coarser levels of energy-wind and mind and making manifest clear light mind so that this clear light mind can be generated as a greatly blissful deep awareness of voidness. Only such awareness can eliminate the obstacles preventing liberation all at once and only such awareness can remove the obstacles preventing omniscience. To rely on a sealing partner as a method of practice without these three types of discernment is a transgression of the tantric vows.