The Pope has condemned "evil" pastors who lay "intolerable burdens" on the shoulders of others which they do nothing to lift. He has called on his priests and bishops to pay attention to "the debates of the time" and the "anguishes" of Catholics.
Pope Francis also said the people of God needed nurturing. He used the biblical metaphor of the fruit in God's vineyard.
"God's dream is his people. He planted it and nurtured it with patient and faithful love, so that it can become a holy people, a people which brings forth abundant fruits of justice," he said.
But in both the ancient prophecy and in Jesus' parable, God's dream is thwarted, he said. "It is the farmers themselves who ruin the Lord's plan: they fail to do their job but think only of their own interests."
Speaking in his homily at St Peter's, Rome at the opening of the Extraordinary Synod on the Family, the Pope said the job of leaders was to nurture the vineyard with freedom, creativity and hard work.
"But Jesus tells us that those farmers took over the vineyard. Out of greed and pride they want to do with it as they will, and so they prevent God from realising his dream for the people he has chosen."
His words will be seen by some as criticisms of over-zealous interpretation of aspects of Catholic doctrine. The Pope is attempting to focus on evangelisation in a Church that is out of step with society on crucial issues such as contraception, marriage and divorce and homosexuality. Many Catholics simply ignore teaching on artificial contraception in particular, which is technically banned. The most pressing issue for many is the refusal to allow remarried divorcees to receive Holy Communion if their previous marriage has not been annulled. This is regarded as cruel and unjust to people such as women who are devout Catholics, but who have been deserted and divorced by faithless husbands.
The Pope said: "The temptation to greed is ever present." He added: "To satisfy this greed, evil pastors lay intolerable burdens on the shoulders of others, which they themselves do not lift a finger to move."
He continued: "Synod Assemblies are not meant to discuss beautiful and clever ideas, or to see who is more intelligent. They are meant to better nurture and tend the Lord's vineyard, to help realise his dream, his loving plan for his people. In this case the Lord is asking us to care for the family, which has been from the beginning an integral part of his loving plan for humanity."
He warned against being tempted to "take over" the vineyard, because of that greed which is always present in us human beings. "God's dream always clashes with the hypocrisy of some of his servants. We can thwart God's dream if we fail to let ourselves be guided by the Holy Spirit. The Spirit gives us that wisdom which surpasses knowledge, and enables us to work generously with authentic freedom and humble creativity."
The homily served to emphasise the theme of modernising the Church's approach to the concerns of its people, which he also spoke about at a vigil on Saturday night. He said: "To seek again what the Lord asks of His Church today, we must lend an ear to the debates of this time and perceive the odor of the people of today, to the point of being impregnated with their joys and hopes, their sadness and anguishes."
There are nearly 200 bishops from around the world at the synod, which lasts for a fortnight. It will be followed by a bigger gathering next year.
Arthur Roche, former bishop of Leeds and secretary of the congregation for divine worship, told the Guardian that despite expectations running high around the world it was "impossible to say at this stage" what to expect from this month's gathering.