Nutter said on Monday 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 that they occasionally may think, but not say. He took the time to note that there were good hard-working people in the city and many upstanding young people.
But, in a fiery and firm 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 from members in the wooden, red-cushion pews.
He continued: "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 need to participate in their children's lives, mentor, discipline and teach them - not just be a "human ATM" or a "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."
He continued: "The immaculate conception of our Lord Jesus Christ took place a long time ago, and it didn't happen here in Philadelphia. So everyone 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 city's young people are good and have 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, Nutter asked the Rev. Albert F. Campbell, Mount Carmel's pastor, who Nutter has known and prayed with for years, for permission to speak.
Nutter preached to a congregation that largely held his beliefs, but he said he hoped they would spread his message citywide.
Nutter grew nine blocks from Mount Carmel. His wife Lisa, who he married 20 years ago last month at Mount Carmel, sat in a front pew next to him. In other pews, some of the women with grand dresses, wearing teal, white, red and other colored hats fanned themselves.
Sitting on 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 sound 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 or firstname.lastname@example.org or @darransimon on Twitter.