Former President Donald J. Trump promised on Monday to join forces with the leaders of the Danbury Institute, a Christian coalition of churches, organizations and conservative activists that wants abortion “eradicated entirely” in the United States.

“Now is the time for us to all pull together and stand up for our values and freedom,” Mr. Trump said in a video address to the organization. “I’ll be with you side by side.”

Mr. Trump did not mention abortion in his remarks. But he promised that the organization would “make a comeback like no other” in a second Trump administration. “These are going to be your years,” he pledged.

“You just can’t vote Democrat — they’re against religion,” Mr. Trump continued. “They’re against your religion in particular.”

The Danbury Institute, which was meeting in Indianapolis as part of the annual meeting of the Southern Baptist Convention, opposes abortion in all cases, including rape, incest and when the mother’s life is at risk. The group has also asserted that life begins at the moment of fertilization, a belief that is commonly used to support restrictions on some kinds of fertility treatments and contraception.

In a panel that preceded Mr. Trump’s address, supporters of the organization urged the antiabortion movement to go further and oppose ballot initiatives that would enshrine abortion rights in state constitutions.

“We need to pressure our legislators to remember that they are under God,” said Tom Ascol, a prominent Southern Baptist preacher. “Jesus Christ rules and reigns in this world. They are accountable to him.”

Not long before Mr. Trump spoke, Al Mohler, the president of Southern Baptist Theological Seminary, pushed for Southern Baptists to, for the first time, issue a resolution opposing in vitro fertilization.

Mr. Trump has sought to take credit for the Supreme Court’s 2022 decision overturning Roe v. Wade, a 6-to-3 decision in which three justices he appointed were in the majority. But he has also said that he would not sign a 15-week federal abortion ban and that he believes restrictions, including whether to prosecute women for abortions or monitor pregnancies, should be left to the states.

The Biden campaign — eager to discuss abortion rights, an issue it believes will motivate women in November — blasted Mr. Trump’s decision to address the organization.

“If you want to know who Trump will fight for in a second term, look at who he’s spending his time speaking to: antiabortion extremists who call abortion ‘child sacrifice’ and want to ‘eradicate’ abortion ‘entirely,’” said Sarafina Chitika, a campaign spokeswoman. “A second Trump term is sure to bring more extreme abortion bans with no exceptions.”