From bishops to religious and the lay community, "All elements of the great mosaic of the church must feel themselves strongly called on by the Lord's mandate to preach the Gospel, so that Christ may be proclaimed everywhere," the pope said in his message for World Mission Sunday.
The annual observance will be marked Oct. 21 at the Vatican and in most countries.
In his message, released in Italian Jan. 25 at the Vatican, the pope said there is a "renewed urgency" for the missionary mandate even as the church celebrates the 50th anniversary of the Second Vatican Council's Decree on the Church's Missionary Activity ("Ad Gentes").
That urgency is based on the increasing number of people around the world who still have not heard the Gospel message and the growing secularism seen in traditionally Christian countries, he said.
"It's necessary to renew enthusiasm for sharing the faith so as to promote new evangelization in traditionally Christian communities and countries that are losing their reference to God, and to help them rediscover the joy of believing," the pope said.
"We need to recover the same apostolic zeal of the early Christian communities who, small and defenseless, were still capable of spreading the Gospel through proclamation and witness," he said.
One of the biggest challenges to evangelization, he said, "is the crisis of faith, not just in the Western world, but among a large part of humankind, which nonetheless hungers and thirsts for God and must be invited and led to the bread of life and living water."
The message's theme, "Called to radiate the word of truth," comes from the pope's apostolic letter "Porta Fidei" ("The Door of Faith"), released last October to formally announce the Year of Faith starting this October.
"Concern for evangelization must never remain on the margins of church activity and the personal lives of Christians;" people of faith need to identify with their faith much more strongly and understand that they are not just recipients but also missionaries of the Gospel, Pope Benedict said.
Given the complexity of the modern world, new ways of communicating the word of God must be found, he said.
Preaching the Gospel effectively in an ever-changing world "requires constantly adapting lifestyles, pastoral plans and diocesan organization to this fundamental dimension of the church's being," that is, evangelization, he said.
"Faith is a gift that was given so that it could be shared," he said; it's "a light that must not stay hidden, but shine throughout the whole house. It is the most important gift ever given in our lives, and we cannot keep it for ourselves."
The pope thanked the work of the pontifical missionary societies, which announce the Gospel by offering "assistance to others, justice for the poorest, the possibility for education in isolated villages, medical care in remote areas, an escape from poverty, rehabilitation for the marginalized, support for human development, a way to overcome ethnic divisions and respect for all stages of life."