“Essential to preparing for marriage is your vocation to chastity. I know that young people reject hypocrisy. You want to be honest with yourselves and others. A chaste person is honest. When God created us he gave us more than one way to “speak” to each other. Besides expressing ourselves through speech, we express ourselves through our bodies. Gestures are like “words” that tell who we are. Sexual actions are “words” that reveal our hearts. The Lord wants us to use our sexuality according to his plan. He expects us to “speak” truthfully. Honest sexual “language” requires a commitment to lifelong fidelity. To give your body to another person symbolizes the total gift of yourself to that person. But if you are not married, you are admitting that you might change your mind in the future. Total self-giving would then be absent. Without the bond of marriage, sexual relations are a lie. . . . Do not be deceived by the empty words of those who ridicule chastity or your capacity for self-control.”

(JPII speaking to the youth in Uganda, quoted in Jason Evert, Saint John Paul the Great: His Five Loves, p.105 Kindle Edition). Full speech here!