Pope St. John Paul II
“Purity as a Christian virtue is revealed in the Pauline letters as an effective way of detaching oneself from what is a fruit of the concupiscence of the flesh in the human heart. Abstaining ‘from unchastity,’ which implies keeping the body ‘with holiness and reverence,’ allows us to deduce that according to the Apostle’s teaching, purity is an ‘ability’ centered on the dignity of the body, that is, on the dignity of the person in relation to his or her own body, to the masculinity or femininity that shows itself in that body. Understood as ‘ability,’ purity is precisely an expression and fruit of life ‘according to the Spirit’ in the full sense of the term, that is as a new ability of the human being in whom the gift of the Holy Spirit bears fruit.”
Source: Pope St. John Paul II, Man and Woman He Created Them, Pauline Books and Media, 2006.