Sex, in Ayn Rand's identification, is "a celebration of [one]self and of existence"; it is a celebration of one's power to gain values and of the world in which one gains them. Sex, therefore, is a form of feeling happiness, but from a special perspective. Sex is the rapture of experiencing emotionally two interconnected achievements: self-esteem and the benevolent-universe conviction.
Sexual feeling is a sum; it presupposes all of a rational man's moral values and his love for them, including his love for the partner who embodies them. The essential meaning of such a feeling is not social, but metaphysical; it pertains not to any single value or love, but to the profound concern involved in all value pursuit: the relationship between a man and reality. Sex is a unique form of answering the supreme question of a volitional being: can I live? The man of self-esteem, using cognitive, conceptual terms, concludes in his own mind that the answer is yes. When he makes love, he knows that yes without words, as a passion coursing through his body.
Sex is a physical capacity in the service of a spiritual need. It reflects not man's body alone nor his mind alone, but their integration. As in all such cases, the mind is the ruling factor.
Leonard Peikoff, Objectivism: The Philosophy of Ayn Rand, p. 344.