It's so important to go to Mass every Sunday because that's where people receive Christ who saves, forgives and unites everyone to his father, church and each other, Pope Francis said.
It's also "important that children are well prepared for first Communion because ... after baptism and confirmation it is the first step toward belonging strongly, really strongly, to Jesus Christ," he said Wednesday at his weekly general audience.
The pope continued a series of talks on the sacraments of Christian initiation, focusing on the Eucharist as the source and summit of the life of the church.
"In fact, every authentic journey of faith, communion and witness springs from this sacrament of love," he said.
The pope began his audience talk by greeting the estimated 13,000 people huddled under umbrellas and raincoats as heavy rain beat down on St. Peter's Square.
"Dear brothers and sisters, good morning, but not good day, huh? It's a bit nasty," he said.
The pope also prayed, at the end of the audience, for all those in Tuscany and Rome affected by severe flooding caused by days of heavy rain.
To help visiting pilgrims who were ill or with disabilities and their caregivers keep warm and dry in the bad weather, the pope said he had them go indoors to the Vatican's Paul VI audience hall to watch the audience on the big screens set up inside.
The pope arrived about 25 minutes later than his usual start time in the square because, as he later explained, he first had gone to greet those pilgrims seated inside the hall.
In his catechesis, Pope Francis said by celebrating the sacrament of the body and blood of Christ, "we participate in the mystery of the passion, death and resurrection of Christ."
"By making himself broken bread for us, the Lord Jesus pours out to us all of his mercy and his love, renewing our heart, our existence and our way of relating to him and our brothers and sisters," he said.
Taking part in the Eucharist "conforms us in a unique and profound way to Christ," he said, granting Christians a foretaste of full communion with God in heaven, "where with all the saints we will have the unimaginable joy of contemplating God face to face."
"We will never thank the Lord enough for the gift he gave us with the Eucharist," the pope said.
"It's such a great gift and that's why it's so important to go to Mass on Sundays," he said.
Mass is a time "not just to pray, but to receive Communion -- this bread that is the body of Christ that saves us, forgives us, reunites us to the father. It's beautiful to do this."
Mass on Sundays is particularly important, he said, because "it is the day of the resurrection of the Lord, and with the Eucharist we feel our own belonging to the church, to the people of God, to the body of God, to Jesus Christ."
At the end of the audience, Pope Francis met and spoke briefly with Lidia Guerrero, the mother of Victor Saldano, an Argentine national who has been on death row in Texas since 1996. Guerrero was accompanied by a representative of the Community of Sant'Egidio, which is active in the fight against the death penalty.