Pope Francis formally opened the synod of bishops Sunday, telling participants that the union between a man and woman is the foundation of God's plan for the family, and a solution to the many forms of loneliness in today's world.

"This is God's dream for his beloved creation: to see it fulfilled in the loving union between a man and a woman, rejoicing in their shared journey, fruitful in their mutual gift of self," the Pope said in his opening Mass for the Synod of Bishops.

He explained that this plan is the same one presented in the day's Gospel for Mark, when Jesus says "From the beginning of creation, 'God made them male and female.'"

"For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh. So they are no longer two but one flesh."

Pope Francis' comments were made during his Oct. 4 Mass marking the official opening of this year's Ordinary Synod of Bishops on the Family.

Set to last from Oct. 4-25, this year's synod follows the theme "The vocation and mission of the family in the Church and the modern world," and follows last year's extraordinary synod on the family, which focused on pastoral challenges regarding family life.

In his homily, Francis noted how the first reading from Genesis, which recounts the story of creation, speaks to us of Adam's experience of solitude before the creation of Eve.

Although Adam was given dominion over the garden and the other creatures, he "felt alone, because there was not found a helper fit for him. He was lonely."

The Pope then pointed to several forms of loneliness in modern society, and said that despite living in a globalized world filled with mansions and skyscrapers, the warmth within families today is diminishing.

While people have great ambitions and many different forms of entertainment, they have little time or freedom to enjoy them, he noted.

"There is) a deep and growing interior emptiness," he said, adding that "the number of people who feel lonely keeps growing, as does the number of those who are caught up in selfishness, gloominess, destructive violence and slavery to pleasure and money."

Like Adam, the world today experiences power but also vulnerability and loneliness, Francis observed, explaining that this fits the image of the modern family.

"People are less and less serious about building a solid and fruitful relationship of love. Love which is lasting, faithful, conscientious, stable and fruitful is increasingly looked down upon, viewed as a quaint relic of the past," he said.

"It would seem that the most advanced societies are the very ones which have the lowest birth-rates and the highest percentages of abortion, divorce, suicide, and social and environmental pollution."

Pope Francis then noted how God was pained by Adam's loneliness when he said that "it is not good that the man should be alone," and created a suitable partner for him.

God's words, the Pope said, "show that God did not create us to live in sorrow or to be alone. He made men and women for happiness, to share their journey with someone who complements them…to love and to be loved, and to see their love bear fruit in children."

Francis referred to how in the Gospel, Jesus was questioned about divorce by the crowd, who practiced and established it as an "inviolable fact," and wanted to trap him.

Jesus responds in "a straightforward and unexpected way" by bringing everything back to the beginning of creation, he said. By doing this, Jesus teaches us "that God blesses human love, that it is he who joins the hearts of two people who love one another, he who joins them in unity and indissolubility."

Turning to the role of the family, the Pope said that Jesus' command to "let not man put asunder" what God himself has joined is an exhortation to believers "to overcome every form of individualism and legalism which conceals a narrow self-centeredness and a fear of accepting the true meaning of the couple and of human sexuality in God's plan."

Francis explained that for God, "marriage is not some adolescent utopia, but a dream without which his creatures will be doomed to solitude! Indeed, being afraid to accept this plan paralyzes the human heart."

Paradoxically, there are many people who ridicule this plan while continuing to be attracted to true, steadfast and faithful love, he said. "We see people chase after fleeting loves while dreaming of true love; they chase after carnal pleasures but desire total self-giving."

Quoting a text by Benedict XVI while he was still Cardinal Joseph Ratzinger, Pope Francis said that in Genesis, "forbidden pleasures lost their attraction at the very moment they stopped being forbidden."

"Even if they are pushed to the extreme and endlessly renewed, they prove dull, for they are finite realities, whereas we thirst for the infinite, he observed.

Francis then said the Church is called to carry out her mission regarding family life in fidelity, truth and love.

In fidelity to her master, the Church is called to defend faithful love and encourage families whose married life reveals of God's own love, he said.

The Church is also called to defend "the sacredness of life, of every life; in defending the unity and indissolubility of the conjugal bond."

He said the Church's mission must be carried out in truth, which doesn't change with passing fads or popular opinions. Truth, the Pope said, "protects individuals and humanity as a whole from the temptation of self-centeredness and from turning fruitful love into sterile selfishness, faithful union into temporary bonds."

Finally, Pope Francis said that for the Church to carry out her mission in charity doesn't mean pointing fingers or judging others, but rather implies being conscious of her duty to seek out and care for wounded couples "with the balm of acceptance and mercy."

Quoting a speech of St. John Paul II from 1978, the Pope stressed that "error and evil must always be condemned and opposed; but the man who falls or who errs must be understood and loved."

The Church, he said, "must search out these persons, welcome and accompany them, for a Church with closed doors betrays herself and her mission, and, instead of being a bridge, becomes a roadblock."

Francis closed his homily by asking the Lord to accompany and guide the Church and the synod fathers during the upcoming discussions, and entrusted the gathering to intercession of Mary and her "most chaste spouse," St. Joseph.