Blake said that the body was the soul's prison unless the five senses are fully developed and open. He considered the senses the 'windows of the soul.' When sex involves all the senses intensely, it can be like a mystical experence.
Sex is full of lies. The body tries to tell the truth. But, it's usually too battered with rules to be heard, and bound with pretenses so it can hardly move. We cripple ourselves with lies.