"The fire set by interests that destroy, like the fire that recently devastated Amazonia, is not the fire of the Gospel," he said before the bishops from the nine countries of the pan-Amazonian region and representatives of indigenous peoples.
"The fire of God is warmth that attracts and gathers into unity. It is fed by sharing, not by profits.
"The fire that destroys, on the other hand, blazes up when people want to promote only their own ideas, form their own group, wipe out differences in the attempt to make everyone and everything uniform."
The global spotlight has recently been on the world's largest rainforest, which is vital for the planet but is suffering from its worst outbreak of fires in years, due in part to an acceleration in deforestation.
The working document for the synod denounced in scathing terms social injustices and crimes, including murders, and suggested a Church action plan.
"Listen to the cry of 'Mother Earth', assaulted and seriously wounded by the economic model of predatory and ecocidal development... which kills and plunders, destroys and devastates, expels and discards," the 80-page document said.
The run-up to the three-week synod, or assembly, saw some 260 events held in the Amazon region involving 80,000 people, in a bid to give the local populations a voice in the document.
Among those attending the synod as an observer was Sister Laura Vincuna, a missionary trying to protect the territories of the Caripuna indigenous people in the Brazilian Amazon.
"Help us defend our motherland, we have no other home!" she said on Saturday.
"Earth, water, forest: without these three elements nobody can do anything," she said on the eve of the synod.