"There resounds in us the multiform cry of creatures: of trees, of rocks, of animals. Everything yearns for fulfillment," he said, quoting St. Paul's words in his Letter to the Romans that "the whole creation has been groaning in travail together until now."
"But we are the only ones to pray consciously, knowing that we are addressing the Father, and entering into dialogue with the Father," he said.
The pope suggested that many people felt ashamed of asking for help.
He said: "Do not be ashamed to pray. 'Lord, I need this,' 'Lord, I am in difficulty,' 'Help me!': the cry, the cry of the heart to God who is the Father."
He continued: "The Lord always gives to us, always, and everything is grace, everything. The grace of God. However, we must not suffocate the supplication that rises up in us spontaneously."
"Prayer of petition goes in step with acceptance of our limit and our nature as creatures. One may even not reach the point of belief in God, but it is difficult not to believe in prayer: it simply exists, it presents itself to us as a cry; and we all know this inner voice that may remain silent for a long time, but one day awakens and cries out."
He emphasized that God will always respond to our supplications.
"There is no prayer in the Book of Psalms that raises a lament that remains unheard," he said. "God alway answers: maybe today, tomorrow, but he always answers, in one way or another. He always answers."
"The Bible repeats it countless times: God listens to the cry of those who invoke Him. Even our reluctant questions, those that remain in the depths of our heart, that we are ashamed to express: the Father listens to them and wishes to give us the Holy Spirit, which inspires every prayer and transforms everything."
He underlined that prayer requires patience and that learning to pray is also learning to wait.
"Now we are in the time of Advent, a time that is typically of expectation; of expectation of Christmas. We are in waiting. This is clear to see. But all our life is also in waiting. Let us learn to stay in waiting; in expectation of the Lord," he said.
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"The Lord comes to visit us, not only in these great feasts -- Christmas, Easter -- but rather the Lord visits us every day, in the intimacy of our heart if we are in waiting. And very often we do not realize that the Lord is nearby, that He knocks on our door, and we let Him pass on by."
He concluded: "Brothers and sisters, staying in waiting: this is prayer."
In his greeting to Italian-speaking pilgrims, the pope recalled that on Dec. 8 he had issued an apostolic letter signaling the start of a Year of St. Joseph that will end on Dec. 8, 2021.
He said: "Yesterday an apostolic letter was published dedicated to St. Joseph, who was declared patron of the Universal Church 150 years ago. I entitled it 'With father's heart.'"
"God entrusted him with the most precious treasures -- Jesus and Mary -- and he responded fully with faith, with courage, with tenderness, 'with a father's heart.' Let us invoke his protection on the Church in our time and learn from him to always do God's will with humility."