Original sentence: The Catechism of the Catholic Church  lists fornication as one of the "Offenses Against Chastity" and calls it "an intrinsically and gravely disordered action" because "use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose
Edited sentence: And 'Self-giving' is necessary for men and women to achieve self-realization and happiness.As an expression of love, sexual intercourse is not something purely biological, but concerns the intimate nucleus of the person.As the encounter of a man and woman, sexual intercourse is intended to nourish and express love.Love is experienced though acts of 'self-giving'.Sex becomes sinful when it's spiritual dimensions are not heeded and the other person is seen as an instrument of one's pleasure instead of as another self.The Catholic view of sexuality is derived from the nature of love