Engaging in or supporting missionary activity allows Christians to enter the "flood of joy" that comes from experiencing God's love and sharing it with others, Pope Francis said.
"The Lord's disciples persevere in joy when they sense his presence, do his will and share with others their faith, hope and evangelical charity," the pope said in his message for World Mission Sunday, which will be celebrated Oct. 19.
In the message, released at the Vatican on Saturday, Pope Francis reflected on the Gospel story of Jesus sending out 72 disciples, two by two, to proclaim the kingdom of God was near.
"The disciples returned full of joy," the pope said, pointing to Luke 10:17.
The disciples, he said, were "excited about their power to set people free from demons. But Jesus cautioned them to rejoice not so much for the power they had received, but for the love they had received."
"The disciples were given an experience of God's love, but also the possibility of sharing that love," Pope Francis said.
In Jesus' day, as in our own, he said, some people cannot accept that love or experience the joy of sharing it with others because they are "too full of themselves" or "claim to know everything already."
The "little ones" of the Gospel, the people who recognize the gift of God's love and share it with others, the pope said, are "the humble, the simple, the poor, the marginalized, those without voice, those weary and burdened, whom Jesus pronounced 'blessed.'"
God's love and promise of salvation in Jesus Christ is the key to eternal happiness, but also the answer to the emptiness and fear that come from a life focused on attaining power and material wealth, Pope Francis wrote.
Christ's disciples are "those who allow themselves to be seized ever more by the love of Jesus" and are "marked by the fire of passion for the kingdom of God and the proclamation of the joy of the Gospel," he said.
Pope Francis said the lack of vocations to the priesthood, religious life or to lay missionary activity in many parts of the world often can be traced to "the absence of apostolic fervor in communities, which lack enthusiasm and thus fail to attract."
"The joy of the Gospel is born of the encounter with Christ and from sharing with the poor," he said. "Wherever there is joy, enthusiasm and a desire to bring Christ to others, genuine vocations arise."
Supporting the church's missionary activity with one's prayers and with financial offerings, the pope said, are a "sign of a self-offering, first to the Lord and then to others; in this way a material offering can become a means for the evangelization of humanity built on love."