July 31, 2013 -- Anti-abortion protestors show up outside of the last surviving abortion clinic in Mississippi, praying and pleading with women not to go inside. They are certain that what takes place there is morally wrong and that God stands with them.

But on the other side of a high fence surrounding the bubble-gum-pink-colored clinic, the staff too believes they have God on their side. They blast music from large boom boxes to drown out the protestors' pleas of "don't kill your baby."

It seemed like a typical day at the Jackson Women's Health Organization in Jackson, Miss., the only place in the entire state where women can get a legal abortion. For more than a decade, the clinic has been the lone abortion provider in Mississippi, a state that has some of the strictest abortion laws in the country.

But this day was different. Everybody on both sides of the fence expected the clinic to be shut down by the state within a few days.

"Nightline" was granted permission to spend 72 hours inside the clinic as its staff grappled with the fear of being shut down for violating a state law that requires its doctors to have admitting privileges at a local hospital -- just the latest in an ever-growing list of regulations designed by state lawmakers, and supported by Mississippi Gov. Phil Bryant, to force the clinic to close.

When local hospitals refused to grant access to the abortion clinic's doctors, the state's Department of Health notified the clinic in January that its state license would be revoked. But this past April, a federal judge extended an injunction to temporarily block the enforcement of the state law, which has allowed the clinic to continue to operate.

But owner Diana Derzis knows her clinic's future is far from certain.

"We are going do everything we can to make it," Derzis said. "We are going be screaming one way or the other. We have to. I mean, you know, we have to. There's no alternative."

Like the protestors, she also believes God is on her side.

"I know as fervently as they do what is moral and right and, if I am wrong, that's between the Lord and I, not them and I," Derzis said.

Derzis knows all too well how dangerous working at an abortion clinic can be. Her first abortion clinic was bombed by Eric Rudolph -- also responsible for the 1996 Summer Olympics bombing -- 25 years ago in Birmingham, Ala. Two people were killed and a nurse was maimed.

"A long time ago, I made peace that it's a possibility that you die," she said. "But, you know, I couldn't imagine a better cause to die for. So I'm fine with that."

Derzis carries a Taser and she owns a gun. She has more security officers and escorts making sure patients get in and out of the clinic safely than other clinic staffers.

Finding doctors willing to work at the clinic is a huge challenge. Derzis said no doctor in the state of Mississippi will work at Jackson Women's Health Organization, so she recruited two out-of-state doctors who fly in every other week.

One of them is Dr. Willie Parker, an OB-GYN who grew up in rural Alabama and now lives in Chicago.

"Diane called me and, at first, I said, 'There's no way I'm going south, growing up in Alabama and knowing how aggressive people can be when they feel strongly about something,'" Parker said.

After visiting the clinic, despite his own deep Evangelical faith, Parker said he felt the women of Mississippi needed him and he changed his mind.

"I felt overwhelmed by the compassion I felt for my patients, and something didn't add up," he said.

Parker said an old Martin Luther King speech about the Good Samaritan finally changed his mind: "While other people passed by the injured traveler in the story and asked, 'What will happen to me if I stop to help this person?' the Good Samaritan reversed the question of concern and said, 'What will happen to this person if I don't stop to help him?'"

Parker is as unapologetic about his work as Derzis, and performs abortions without having hospital admitting privileges -- because no local hospital would give them to him.

He is aware of the danger every time he pulls in to the clinic parking lot, where he is escorted by security through a back door.

"The moment that I drive into the parking lot, I always have what I call the 'bubble guts,'" he said. "I've kind of made my peace with people being verbally aggressive. They have said some very obnoxious things to me, like, 'negro abortionist,' that I kill my race. I'm used to that."

In the next two days, Parker will counsel more than 50 women and performed 30 abortions, telling a room full of patients at one point, "Just because you are in Mississippi, you shouldn't have less rights than someone in California."

"My goal is to see a woman as often as I need to, to make sure that every pregnancy is a planned pregnancy, and every child's a wanted child. So I say, 'How many abortions? As many as necessary.'" Parker said. "When a woman chooses and decides that she needs an abortion ... there needs to be a safe place for her to have one."

All of the patients "Nightline" spoke to declined to appear on camera.

One young woman, off-camera, said, "I don't regret it, and I know that sounds selfish ... but I did what's best for me.

"I'm a good person," she added. "You cannot judge a situation until you're in it."

Among the choruses of, "Jesus loves you and your baby," and, "Ma'am, don't kill your baby today" from the protestors, Cal Zastrow's voice booms louder than most. The veteran anti-abortion rights activist is a familiar face outside the clinic's fence. Two of his four children, 19-year-old Corey and 17-year-old David, protest with him almost every day.

"We always bring baby shampoo. It helps wash out the pepper spray from your eyes," Zastrow said, referencing his many run-ins with the police and with clinic workers around the country.

Zastrow's children are homeschooled and as long as they can remember the Zastrows have spent their lives on the road, traveling around the country in their dusty, wine-colored Honda.

"I serve and volunteer with ministries," Zastrow said. "Sometimes, I have temp jobs as a consultant -- political campaigns, strategy PR, those kind of things."

Zastrow and fellow protestors said they weren't fazed by the federal judge's ruling to keep the clinic open, for now.

"It's not a setback for our mission, it's a setback for families and babies killed here every day," said Chet Gallagher, a former police officer who was fired 20 years ago for refusing to arrest anti-abortion rights protesters. He has been protesting full-time ever since.

"We don't verbally assault. We offer help and preach the gospel," said Zastrow, countering claims by Derzis and clinic staff that they "harass" women leaving the clinic after procedures.

But Derzis countered right back.

"When [patients] come out and you're screaming, 'How's it feel to have killed your baby?' Man, that's a bad person. There's nothing Christian about that," Derzis said.

Anti-abortion advocates who protest outside of the clinic argue that there is nothing safe about abortions, and say they are outraged that people like Parker won't concede the basic biological fact that if the fetus is left unimpeded, a baby will be born.

Their goal is to get women to reconsider the abortion, and when they are successful, one of the people they refer women to is Barbara Beaver, who runs a crisis pregnancy center on the other side of town.

Beaver offers counseling and support to women with unexpected pregnancies. The facility is stocked with baby food and clothes.

"So many of them say, 'Because it was legal, I thought it was right,'" Beaver said. "We have sanitized abortion. We can't go back to the coat-hanger days, so we don't call them coat hangers anymore. We call them cannulas. That cannula does the same thing to the baby that the coat hanger did. It's just sanitized."

Beaver believes all women will regret having an abortion in some part of themselves, but Derzis said that Beaver is "absolutely wrong," pointing out that an estimated one in three American women have had an abortion -- that according to a 2008 study by the non-profit Guttmacher Institute.

"My experience [is] that women who make this decision [do so] knowing full well they have choices," Derzis said.

But on the eve of a decision that will determine whether women can receive legal abortions in Mississippi, tensions, on both sides, flared. Find out what happened on "Nightline" TONIGHT at 12:35 a.m. ET.