VATICAN CITY (CNS) — Christianity is not a set of prohibitions, but a “project for life” that can lead to true happiness in building better relationships and a better world, Pope Francis told Catholic young people.

“Do you realize how much you are worth in the eyes of God?” the pope asked youths in his annual message for local celebrations of World Youth Day. “Do you know that you are loved and welcomed by him unconditionally?”

The ability to love and be loved is beautiful and is a key to happiness, but sin means it also can be “debased, destroyed or spoiled” by selfishness or the desire for pleasure or power, he said in the message, published Feb. 17 at the Vatican. (Also in Spanish.)

In preparation for the next international celebration of World Youth Day, which will be held in Krakow, Poland, July 25-Aug. 1, 2016, many dioceses will have their own celebrations Palm Sunday, March 29.

The Poland gathering will focus on the beatitude from St. Matthew’s Gospel, “Blessed are the merciful, for they will be shown mercy.” The 2015 theme chosen by Pope Francis is the beatitude, “Blessed are the pure in heart, for they shall see God.”

The “beatitude” or blessedness for which God created human beings and which was disrupted by the sin of Adam and Eve “consists in perfect communion with God, with others, with nature and with ourselves,” the pope wrote. God’s “divine light was meant to illuminate every human relationship with truth and transparency.”

But with sin, he said, Adam and Eve’s relationship with each other, with God and with creation changed. “The inner compass which had guided them in their quest for happiness lost its point of reference and the attractions of power, wealth, possessions and a desire for pleasure at all costs led them to the abyss of sorrow and anguish.”

God still loved the human creatures he created and still wanted them to find happiness, the pope said, so he send his son to become one of them and to redeem them.

Jesus taught that impurity or defilement was not something that happened because of what someone ate or who they touched, but was something that came from inside the person. Jesus listed “evil thoughts, fornication, theft, murder, adultery, coveting, wickedness, deceit, licentiousness, envy, slander, pride, foolishness,” the pope said, pointing out that most of the things on the list have to do with a person’s relationship with others.

“We need to show a healthy concern for creation, for the purity of our air, water and food,” the pope told young people, “but how much more do we need to protect the purity of what is most precious of all: our heart and our relationships. This ‘human ecology’ will help us to breathe the pure air that comes from beauty, from true love, and from holiness.”

Pope Francis said he knows “your desire for a love which is genuine, beautiful and expansive” is beginning to blossom. It is such a powerful gift of God that it must be protected and nurtured with care.

“Do not let this precious treasure be debased, destroyed or spoiled,” he said. “That is what happens when we start to use our neighbors for our own selfish ends, even as objects of pleasure. Hearts are broken and sadness follows upon these negative experiences.”

“Rebel against the widespread tendency to reduce love to something banal, reducing it to its sexual aspect alone, deprived of its essential characteristics of beauty, communion, fidelity and responsibility,” the pope wrote. “Rebel against this culture that sees everything as temporary and that ultimately believes you are incapable of responsibility, that believes you are incapable of true love.”

Church teaching about love and sexuality, he said, is not a series of prohibitions, but a push to rebel against temptation and worldly imitations of love in order to find the real thing: a lifelong, life-giving commitment.

Through prayer, speaking to Jesus “as you speak to a friend,” and reading the Bible, he said, people can draw closer to God and allow him to purify their hearts, discovering God’s call to live a life of love in marriage, the priesthood or religious life.