On Dr. Martin Luther King Jr.’s birthday Sunday — and four days before Inauguration Day — members of Community Church of Boston were reminded of a letter the civil rights leader sent to the church decades ago. In it, he praised the church’s focus on peace, justice, and human rights.

Members of the nearly century-old congregation said their mission is more important than ever as Donald Trump’s administration prepares to take office.

And King’s words remain to spur them forward.

“I feel it’s going to be a time to stand up and do the right thing,’’ said Tillyruth Teixeira, 85, of Boston. “To stand on principle and not let anyone tell you to shut up.’’

Charles Yancey, a former Boston city councilor, gave the Martin Luther King Lecture Sunday at the church in Copley Square. He focused­ on how far the nation has come in addressing racial ­inequality and how far it still needs to go. Standing before a mural depicting diverse faces and bearing the words “Justice’’ and “Peace,’’ he said that if King were alive he would tell the nation to take heart.

“[King] would say that even though Donald Trump is taking Barack Obama’s place in the White House that we should not be discouraged. That we should use history as our guide,’’ Yancey said.

“He would tell you, you survived the colonial rule in the streets of Boston, that Crispus Attucks did not give his life in vain. He would remind you that in spite of the oppression we were still able to produce a Phillis Wheatley. He would tell you very clearly that we in the city of Boston have a lot to be thankful for, we in this country have a lot to be thankful for.’’

He reminded the church King wasn’t welcomed with open arms, especially after he criticized Boston for its segregation, particularly in housing, employment, and education.

Yancey said King encountered racism as a student when apartments he tried to rent were denied to him and when he was told there were no vacancies. Yet, white students who applied for the same places would be successful.

“The city of Boston accused him of being a troublemaker and an agitator because he saw the inequities, he saw the injustice, he saw that the status quo in the city of Boston needed as much attention as Montgomery and Birmingham,’’ Yancey said.

Yancey mentioned modern-day challenges such as police brutality and the limitations of local public schools. He said King would have continued to challenge the status quo and advocated for a civilian review board to provide oversight and body cameras for police officers.

“While many then and today view the city of Boston as a utopia, as a place where people are open-minded, not just tolerant, but people who will fight for justice,’’ Yancey said. “We must remember we have other elements in the city of Boston who really want to turn the clock back.’’

Dean Stevens, 61, of Brookline, a longtime member of the church, said he’s been dreading this week since Trump was elected on Nov. 8. But he wondered if Trump’s election might be the motivation progressives need to organize and unite. The situation reminded him of a quote by American abolitionist and reformer Theodore Parker that King adapted in one of his speeches: “The arc of the moral universe is long, but it bends toward justice.’’

Josh Rosen, 61, of Roslindale, one of two musicians who played during the event Sunday, was 8 years old when he went to Washington, D.C., with his parents and heard King give his now-famous “I Have a Dream’’ speech. He said he remembers how riveted the crowd was.

These days, he said, he performs the protest song “We Shall Overcome’’ differently on the piano, changing a major chord to a minor one, adding a twinge of sadness and uncertainty to the normally strong anthem.

Yancey’s speech lifted the spirits of Christle Jackson, 56, the church’s office and publications manager. She remembered being a young girl in Framingham and encountering hurdles as part of the only black family in the neighborhood.

“We still have all these challenges,’’ Jackson said. “But it has changed; it is better. We just have a lot of work to do.’’

Her husband, Reginald Jackson, 72, said he looks to King as a source of inspiration to persevere.

“That’s the lesson I take from his life,’’ he said. “And his connectedness to community.’’

Cristela Guerra can be reached at cristela.guerra@globe.com. Follow her on Twitter @CristelaGuerra.