Nutter said he would outline elements of a broad plan - which he called a "more holistic approach" - to crack down on flash mobs and address the needs of young people and families.
"Some will be positive," Nutter told the congregation. "Some of them you won't like."
Before his roughly 30-minute speech, Nutter warned church members that he would say things they occasionally may think but not utter. He noted that there were good, hardworking people in the city and many upstanding young people.
But, in a fiery speech that elicited applause, praise, and chuckles, he condemned young people involved in flash mobs, saying they will be punished. He scolded neglectful parents, particularly some African American fathers, challenging them to be more involved.
"Parents, get your act together," he said to applause. "You need to get hold of your kids before we have to."
He said neglectful parents would face criminal charges.
Nutter, a father of two, including a teenage daughter, said men needed to participate in their children's lives and mentor, discipline, and teach them - not just be a "human ATM" or "sperm donor." "That's not good enough. You can do better than that."
"A particular problem in the black community is we have too many men making too many babies that they don't want to take care of," he preached to applause. "We end up dealing with your children.
"The immaculate conception of our Lord Jesus Christ took place a long time ago, and it didn't happen here in Philadelphia. So every one of these kids has two parents who were around and participating at the time. You need to be around now.
"Ain't no immaculate conception happening up in here."
He said 99 percent of the city's young people were good and had good intentions.
But "there are some really bad ones," he said. "They're lawless. They act with ignorance. They don't care about anybody else, and their behavior is outrageous. Well, we're not going to tolerate that."
Nutter, who said he had not been at a Sunday service at Mount Carmel in several months, later called his message "personal."
On Friday, he asked the Rev. Albert F. Campbell, Mount Carmel's pastor, whom he has known and prayed with for years, permission to speak.
Nutter preached to a congregation that largely shared his beliefs, but he said he hoped its members would spread his message citywide.
The mayor grew up nine blocks from Mount Carmel. His wife, Lisa, whom he married 20 years ago last month at Mount Carmel, sat in a front pew next to him.
Sitting in the balcony, as she does each Sunday, Norma Newberry said Nutter's message was poignant.
"The most important thing is parents have to start parenting," said Newberry, who was baptized at Mount Carmel in 1951.
At one point during his speech, Nutter heard what sounded like a child's praise from the congregation.
"I heard a child say, 'Amen.' Some of them [are] smarter than some of these adults running around here," he said.
Contact staff writer Darran Simon at 856-779-3829, email@example.com, or @darransimon on Twitter.