While isolation, social distancing and economic uncertainty caused by the COVID-19 pandemic prove to be a challenge, Christians are called by God to take part in the church's mission in the world, Pope Francis wrote in a message for World Mission Sunday 2020.

"The impossibility of gathering as a church to celebrate the Eucharist has led us to share the experience of the many Christian communities that cannot celebrate Mass every Sunday," the pope wrote in his message, which was released by the Vatican May 31.

"In all of this, God's question: 'Whom shall I send?' is addressed once more to us and awaits a generous and convincing response: 'Here am I, send me!'" he said.

World Mission Sunday will be celebrated Oct. 18 at the Vatican and in most dioceses.

In his message, the pope said that despite the suffering and challenges posed by COVID-19, the church's "missionary journey" continues. Although pain and death "make us experience our human frailty," it also serves as a reminder of "our deep desire for life and liberation from evil."

"In this context, the call to mission, the invitation to step out of ourselves for love of God and neighbor presents itself as an opportunity for sharing, service and intercessory prayer," he wrote. "The mission that God entrusts to each one of us leads us from fear and introspection to a renewed realization that we find ourselves precisely when we give ourselves to others."

To be a "church on the move," he explained, is neither a program nor "an enterprise to be carried out by sheer force of will," but rather follows the prompting of the Holy Spirit "who pushes you and carries you."

Pope Francis said the celebration of World Mission Sunday offers an opportunity to reaffirm that one's prayers, reflections and offerings are ways "to participate actively in the mission of Jesus in his church."

He also reminded Christians that the mission of evangelization is "a free and conscious response to God's call" that can only be discerned by one's "personal relationship of love with Jesus present in his church."

"In all of this, God's question, 'Whom shall I send?' is addressed once more to us and awaits a generous and convincing response: 'Here am I, send me!'" the pope said. "God continues to look for those whom he can send forth into the world and to the nations to bear witness to his love, his deliverance from sin and death, his liberation from evil."