"Nobody can pretend any longer what this is all about."
The church meeting was the first time 77-year-old Mr Biden, who served as president Barack Obama's vice president, had participated in person in a public gathering since mid-March, when the COVID-19 pandemic abruptly paralysed his campaign.
"Hate just hides. Doesn't go away. And when you have somebody in power who breathes oxygen into the hate under the rocks, it comes out from under the rocks," Biden said of Trump.
"It matters what the president says," Mr Biden added. "It encourages people to bring out the vitriol."
Later, speaking at a virtual town hall, Mr Biden returned to the theme of racism.
"There is systemic racism, white supremacy, it's real," he said. "You see it. I think we all see it but African-Americans see more clearly."
The death of Mr Floyd - a black man killed in Minneapolis, Minnesota while in police custody - "invoked the full weight of our history ... how black lives have been devalued by society. And it's not only intolerable but people are angry," he said.
Mr Biden's remarks came after days and nights of demonstrations and riots around the country over the death of Floyd, filmed as he was pleading for air while his neck was under the knee of a white police officer.
Promise for first 100 days
Inside the Bethel AME church, which has a black congregation, Mr Biden wore a mask and took notes after a prayer was said.
Leaders and congregation members criticised Mr Trump, but also challenged Mr Biden to do more for African Americans if he wins the White House in November.
Democratic House Representative Blunt Rochester, in emotional, impassioned remarks, said she appreciated Biden for "showing up."
"For those who are out there complaining, we've got a president that ain't even showing up, that doesn't even care," she said. "Come on."
But State Senator Darius Brown noted that African-Americans did not gain economically during the eight years of Biden's vice presidency.
"We're here not only to love you, but to push you" for more support to the Democratic Party's African-American base, he said.
Mr Biden said he would work in his first hundred days of office to address the needs of black Americans.
"I promise you .... that we're going to make sure that the economic recovery deals with the institutional structures and institutional racism, but also economic structures that need to be fixed," he said.
Mr Biden promised the black leaders at that, if elected in November, he would create a police oversight commission in his first hundred days in office.
Several people urged Mr Biden to choose an African-American as his vice-presidential running mate.
"I promise you there are multiple African-American candidates who are being considered," he said.