The perfect marriage in many ancient traditions has been said that is between god and goddess. In modern times this may be seen as man and woman but there is more to sex in sacred sexuality. Sacred sexuality is a form of abandoning ones own Ego to unite with your consort/beloved in the most sacred way. This brings both people into a state of bliss, happiness and joy and increases vitality in the body. The beginning of these mysteries should begin with the views of the Gnostic Christians in early faith, which are said to hold the "inner mysteries" and keys of this sacred connection.
Right now we are seeing a lot of people connecting to their inner Divine Feminine and Divine Masculine aspects. This is done through mantra, yoga and other holistic and natural practices. All of this new age inner work is really a transformation that Gnostics always knew about and are still on the path to co-creating with us a new world where peace resides. The sacred marriage begins with the tale of Sophia and her counterpart the Christ. "The myth of the "fall of Sophia" is a reflection of the "fall of Adam and Eve". In both the ultimate heartbreak occurs where we become separate from the Divine. This story reflects our fall as a humanity, into duality (where God has fallen asleep within us). This is the separation of the body/Ego from the realized Self which happens through Self Awareness. The mystical marriage signifies that both the Ego/body and the Self come together in unity returning us to the Garden of Eden.
The way to the Sacred Marriage in modern times is to be faithful to your one beloved consort. This is the way to harness the Christification of ourselves. Becoming man and woman into God and Goddess. So what is Christification? Well that is becoming Godly as in not being driven by Ego desires and becoming closer to Divinity then human. Like Christ, it is transmuting the mind to a divine mind and body into unity with the Divine (as in Yoga).
In this kind of Yoga , or divine union, the Sacred Marriage brings us back from our earthly incarnations into more divine spirit within being manifested in our daily reality. Loosing identification with the "false self" and being identified with your Christ self. As Timothy Freke and Peter Gandy say, "'When we experience the mystical marriage we become aware of ourselves as being. We are at rest, the still center of the turning world of appearances."' As the world that we know we do not have many relationships that serve this goal. This is the true reasons what sex is meant to be for, the connection of two souls on a path of Gnosis, of purity, of Yoga, of Light.