We know that the sexual appetite in us humans can be strong and that it is often manipulated for profit. It's well known that sex sells. The advertisement and entertainment industries, among other enterprises, take advantage of the disorder in us caused by original sin. Conjugal relations belong exclusively to marriage because their purpose is both procreation and mutual permanent love. That's the way God designed it for us from the beginning. He made us male and female and said to be fruitful and multiply (Gn. 1:28). This was the institution of marriage. However, Adam and Eve sinned; they disobeyed God. Things went awry. So, a disorder ensued. Among other things the abuse of sex occurred.
The virtue of chastity is that capacity we have to understand and use our sexual powers properly. This involves not only our body but also our mind and heart. Jesus said that it's not only the act of adultery that is a sin but also looking at another lustfully is also the sin of adultery (Mt. 5:28). Therefore we should avoid those thoughts, desires and affections which are not appropriate to our state in life. Without chastity it is not possible to have true human love nor to love God. Without this virtue, a person becomes a slave to his or her passions and can easily be reduced to the animal state, existing merely for the pleasures of the flesh.
Chastity is a positive strength. It is only those, who promote sexual license, believe that it is an unfair restriction. It is meant for everyone. It's for married people as well as those who are single. It engenders true selfless love and mutual respect. It promotes the dignity of each person. If it is removed from the conjugal act, then sexual relations are nothing more than acts of selfishness. They are good so long as they please the persons involved. Too often this leads to unhappy marriages and divorce.
Charity is the greatest of virtues. Yet, without the virtue of chastity there cannot be real love. In the marital state couples encounter God in the proper fulfillment of their duties as loving spouses. For those who are in the celibate state of the priesthood and/or religious life, chastity means having an undivided heart that is given only to God and His work. For those who are single, it means respecting the bodies of others as well as their own bodies and not enjoying the relations proper to marriage.
It's no surprise that God's plan for us to live chastely is completely foreign to most people. But such was the case when Jesus walked the earth and when the Church was born. Yet, Christians faithful to our Lord's teaching were able to convert much of the world. Why? Because they spoke the truth - the truth that spoke to the hearts of the people then. This is the same eternal truth that speaks to our hearts.