Pope Francis, in his address to Congress Thursday, repeatedly cited the example of two American Catholics – Thomas Merton and Dorothy Day – figures who often have been on the fringes of the Church, but whose legacies have been thrust back into the spotlight by Francis. 

Including Day and Merton alongside classic American historical figures like Martin Luther King Jr. and Abraham Lincoln, the Argentinian pontiff cited the pair as examples for Catholics and lawmakers to follow. Both were known for their keen interest in social justice and dialogue with other religions, which frequently caused them to clash with church authorities.

“Merton was above all a man of prayer, a thinker who challenged the certitudes of his time and opened new horizons for souls and for the church.  He was also a man of dialogue, a promoter of peace between peoples and religions,” Francis said.

Merton (1915-1968), a Catholic convert who became a Trappist monk, was known for his spiritual writings which often blended Buddhist and Taoist spirituality into his writings, and frequently delved into social issues of the time. Merton was a staunch opponent of the war in Vietnam and outspoken about racism in America – famously writing a powerful poem about children protesting racism in Birmingham, Alabama facing police dogs and angry mobs. (“And the children of Birmingham walked in the shadow of Grandma’s devil.”)

“Merton became more and more aware of issues in the world outside the monastery and outside the church, in that he began to be very provocative in the things he would say, such as working for justice and peace, he was a strong critic of Vietnam, he opened up avenues of dialogue with other religions, and wanted to preserve the environment," Abbot James Wiseman of St. Anselm’s Abbey in Washington, D.C., told FoxNews.com.

Wiseman says that a key aspect of Merton’s spirituality was dialogue with other faiths, and he believes this is why Francis chose to mention him in his address.

“In his talk, Francis used that word ‘dialogue’ and Merton was a pioneer of dialogue with people of other persuasions,” Wiseman said.

However, that frequently made Merton the subject of criticism as he became a widely read author with best-selling books such as "The Seven Storey Mountain."

“A lot of criticism, especially in his last ten years, was by people who thought monks should speak only on ‘church-y’ topics, and it wasn’t his business to speak about Vietnam or American racism or other social issues,” Wiseman said.

Day (1897-1980) was also praised by Francis during his address:

“In these times when social concerns are so important, I cannot fail to mention the Servant of God Dorothy Day, who founded the Catholic Worker Movement. Her social activism, her passion for justice and for the cause of the oppressed, were inspired by the Gospel, her faith, and the example of the saints,” Francis said.

Day, now on a path to sainthood, also walked into similar controversies. A figurehead for the Catholic left and a pacifist during World War II, Day was frequently labeled a socialist and an anarchist  after founding the Catholic Worker Movement in the 1930’s and taking left-wing positions on a number of issues including unions, poverty and opposing war.

"I think Dorothy Day and Thomas Merton clearly recognized that to be a faithful member of the church, it includes and even requires being concerned with issues that go beyond the church door.”

- Abbot James Wiseman

Day became a target for figures on the right, earning herself the nickname “Moscow Mary,” with National Review founder William F. Buckley slamming the “slovenly, reckless, intellectually chaotic, anti-Catholic doctrines of this good-hearted woman.”

Day’s supporters say that, while she embraced Marxism as a young woman, she later rejected it after her conversion, although she remained firmly attached to many left-wing causes.

“She’s certainly in her life had an evolution, attracted to communism as a child but later in life devoted to Catholic social justice teaching, and she made that come alive and pushed the institutional church to more than it already was doing. And I think that made some people more uncomfortable than they’d like,” Rev. Raymond Studzinski, associated professor of spirituality at the Catholic University of America, told FoxNews.com.

Day was arrested numerous times at pro-labor and anti-war protests, and was a great believer in civil disobedience to advance political beliefs. However, Studzinski believes that Day’s inclusion is less about politics than making reference to two prominent and influential American Catholics.

“I think it reflects his sensitivity to the group he’s speaking to in terms of people and people who are on the spiritual landscape. He’s trying to address a particular church and having something to say to Catholics in a particular church,” Studzinski said.

Wiseman, however, notes that both were active beyond purely religious issues and thinks this is the message Francis was trying to communicate.

“In a nutshell I think Dorothy Day and Thomas Merton clearly recognized that to be a faithful member of the church, it includes and even requires being concerned with issues that go beyond the church door,” Wiseman said.

“It's not only possible, but also proper, for a Catholic or a member of any other religious tradition to be concerned with justice, peace in the world, understanding of other faiths and concern for the environment. [Pope Francis] is putting on record that what he’s doing is not all that new,” he said.

Adam Shaw is a Politics Reporter and occasional Opinion writer for FoxNews.com. He can be reached here or on Twitter: @AdamShawNY.