PHILADELPHIA (CNS) -- The first symbol of God's creative love is when he said, "Let there be light," because light encourages good and darkness encourages evil, Cardinal Robert Sarah said at the World Meeting of Families in Philadelphia.

Light brings order out of darkness and love out of chaos, he said in a Sept. 23 keynote.

The second great symbol, the pinnacle of God's creation, comes when God said, "let us make man in our own image and likeness," added Cardinal Sarah, who spoke on the topic "The Light of the Family in a Dark World."

Formerly the archbishop of Conakry, Guinea, and past president of his country's conference of Catholic bishops, the cardinal is currently prefect of the Vatican's Congregation for Divine Worship and the Sacraments.

The family, Cardinal Sarah said, is like the Trinity, which is one in nature but with distinct persons: Father, Son and Holy Spirit. In this perfect unity we find the nature of God, which is love.

Man was created for fellowship with God, and God made woman because God said, "It is not good for man to be alone." This formed the first human family, each member equal in dignity and complementary in relationship.

Each was called to make a gift of himself or herself for the other in imitation of God himself.

The fall from grace, as told in the Book of Genesis, wants us to understand how darkness slowly seeped into the goodness of God's creation, said Cardinal Sarah, who explained how Adam and Eve broke the relationship with God by disobeying his command.

"Sin generates death, not just physical death but death of being," he said. "We are all capable of sin but God reached out in mercy to man and woman. The healing of the family was accomplished when God sent his Son into the world.

"You and I are subject to death because of sin," Cardinal Sarah said. "Yet we do not die because Jesus takes our place. Jesus affects the union between God and man when Jesus breaths his last words."

Together, the Father and the Son send into our hearts the Holy Spirit, the giver of life, and God chose the family as the means to transmit God's love, Cardinal Sarah explained.

"The family is called to live this relationship; husband and wife, parent and children and grandchildren," he said. "In the family we learn to relate, to love and serve one another. The world today needs heroic witnesses to defend the family."

In a world that has forgotten God, he said, and where the light of faith is in danger of being snuffed out entirely, Christian families are called to bring their witness of love and fidelity, thereby evangelizing the world.

It is in the family where we learn to love and relate, he said, where selfishness is overcome and the love of God is made real and becomes the center of our lives.

At several points in his keynote address, the audience burst into applause. "All those wounded by personal sin and the sin of others ... the divorced and separated ... can and must find in the church a means of regeneration without fear of being pointed out," he said.

Cardinal Sarah closed his address by highlighting the story of a family with 10 children who lived their faith in a dynamic way. The father was a firefighter who was killed on 9/11. Jean, the mother, said in an interview that the terrorist attacks were a great evil, but that the love of God was greater and that "God works for the good of those who love him." She said she prayed that God would forgive the terrorists.

Two years ago, Jean died from cancer and her eight sons carried her casket into the church. People noticed that the 15-year-old daughter, Maggie, seemed to have great peace. She told them that she knew her mother was in heaven and was experiencing perfect joy. "What more could I want for her?" she told people. The eldest son, Anthony, will soon be ordained to the priesthood.

"This is how God has worked from the beginning of creation," Cardinal Sarah said. "God overcomes evil with good."

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Baldwin writes for CatholicPhilly.com, the news website of the Archdiocese of Philadelphia. Contributing to this story was Tony Gutierrez, editor of The Catholic Sun, newspaper of the Diocese of Phoenix.