Pope Leo urged the world's Catholics to help immigrants in his first major document, which was released on Thursday and invoked one of the late Pope Francis' strongest criticisms of President Donald Trump's anti-immigration policies.

Leo's document, known as an apostolic exhortation, is focused on the needs of the world's poor. It calls for widespread changes to the global market system to address rising inequality and to help people living paycheck-to-paycheck.

The 104-page text started as a writing project by Francis, who was unable to complete it before his death in April after 12 years leading the global Church of 1.4 billion people. It was finished by Leo, the first U.S. pope.

"I am happy to make this document my own – adding some reflections – and to issue it at the beginning of my own pontificate," Leo writes at the beginning of the text.

Elected in May to replace Francis, Leo has shown a much more reserved style than his predecessor, who frequently criticized the Trump administration.

But Leo has been ramping up his disapproval in recent weeks, drawing heated backlash from some prominent conservative Catholics.

"The Church, like a mother, accompanies those who are walking," the pontiff writes in the document, titled "Dilexi te" (I have loved you). "She knows that in every rejected migrant, it is Christ himself who knocks at the door of the community."

"Where the world sees threats, (the Church) sees children; where walls are built, she builds bridges," Leo says, referencing Francis' 2016 criticism of Trump as "not Christian" because of the president's plan in his first term to build a wall on the U.S.-Mexico border.

The White House has said Trump was elected based on his many promises, including to deport "criminal illegal aliens."

The number of people living in poverty "should constantly weigh upon our consciences," the document said.

"There is no shortage of theories attempting to justify the present state of affairs or to explain that economic thinking requires us to wait for invisible market forces to resolve everything," it said.

"The poor are promised only a few 'drops' that trickle down, until the next global crisis brings things back to where they were."

The document signals that Leo shares some of the same priorities of Francis, who shunned many of the trappings of the papacy and frequently criticized the global market system as not caring for society's most vulnerable people.

"The illusion of happiness derived from a comfortable life pushes many people towards a vision of life centered on the accumulation of wealth and social success at all costs, even at the expense of others," the text says.

"Either we regain our moral and spiritual dignity or we fall into a cesspool."