(CNN) Jim Obergefell sat in the Supreme Court on a June morning more than two years ago and listened as Justice Anthony Kennedy read an opinion that would re-shape the lives of LGBT Americans by clearing the way for same-sex marriage nationwide.

"They ask for equal dignity in the eyes of the law. The Constitution grants them that right," Kennedy wrote in the opinion.

"Sitting in the court room, once it finally stuck that Justice Kennedy was saying we had won," Obergefell remembered in a recent interview. "I realized for the first time in my life as an out gay man, that I felt like an equal American."

Since the opinion, Obergefell -- the lead plaintiff in the case -- says he's been stopped in the street and at times thanked by supporters for the fight he waged. "That decision for them represented our nation getting it right. Something that doesn't always happen."

Another Supreme Court term is set to begin in October, however, and there will be a new plaintiff in town.

Masterpiece Cakeshop

Jack Phillips is bringing a different LGBT-related fight to the highest court in the land, and he hopes the justices will deliver a victory to like-minded people who say they are waging a fight for religious liberty.

Phillips -- who owns a bakery in Colorado called Masterpiece Cakeshop -- argues he can't be compelled to violate his sincerely held religious beliefs and create and decorate a cake for a same-sex couple to celebrate their marriage.

Two plaintiffs -- past and present -- will watch this term to see how the Supreme Court handles the language of Obergefell v. Hodges.

To be sure, the core holding of the landmark case is not in jeopardy. But supporters of LGBT rights fear the court could chip away at its principles concerning equality and dignity. And opponents place emphasis on the parts of Kennedy's opinion that stress respect for "those who adhere to religious doctrines."

Masterpiece Cakeshop v. Colorado Civil Rights Commission is the "next logical step" after Obergefell, said University of Chicago Law School professor William Baude, adding the case "will feature arguments about how broadly the principles of Obergefell reach both in the law and society as a whole."

"The question is whether Obergefell was supposed to end the conversation with a definitive victory for one side, or whether there are still further questions to fight over," Baude said.

Chief Justice John Roberts wrote a dissent in Obergefell and foreshadowed future challenges.

"Hard questions arise when people of faith exercise religion in ways that may be seen to conflict with the new right to same-sex marriage" the chief wrote.

Indeed, Phillips' faith is central to the upcoming arguments. One of his lawyers, Jeremy Tedesco of the Alliance Defending Freedom, said the new case -- that began before gay marriage was legalized nationwide -- will "test" the language of Obergefell.

"That people who disagreed with the redefinition of marriage, would be able to continue to believe that marriage is between a man and a woman and act on those beliefs," he said.

All the way back to 1993, when Phillips decided to open his bakery, he knew there were certain kind of cakes he would not want to make in order to abide by his religious beliefs.

"We didn't want to make cakes for Halloween, for example," Phillips said. He and his wife also knew that they wouldn't want to make cakes to celebrate same-sex marriage because their Christian faith teaches them that marriage should be between one man and one woman.

Flash forward to 2012 when same-sex marriage was not yet legal in Colorado, but two men walked into the bakery.

"The conversation was fairly short," Philips remembered. "I went over and greeted them. We sat down at the desk where I had my wedding books open."

The men -- David Mullins and Charlie Craig -- told Phillips they wanted a cake to celebrate their planned wedding that would be performed in another state.

Phillips says he knew right away that he couldn't create the product they were looking for without violating his faith.

"The Bible says 'in the beginning there was male and female,'" he said.

For Phillips, his religious beliefs guide his decisions in every aspect of his life. So he cannot, in good conscience, create a cake for an event he says contradicts God's teaching, he said.

He offered to make any other baked goods product for the men.

"At which point they both stormed out and left," Phillips said.

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Previous ruling

The couple filed a complaint with the Colorado Civil Rights division, which ruled in favor of them citing a state anti-discrimination law. Phillips took his case to the Colorado Court of Appeals arguing that requiring him to provide a wedding cake for the couple violated his constitutional right to freedom of speech and free exercise of religion.

The court held that the state anti-discrimination law was neutral and generally applicable and did not compel Masterpiece to "support or endorse any particular religious view." It prohibited Phillips from discriminating against potential customers on account of their sexual orientation.

Louise Melling, an ACLU lawyer representing Mullins and Craig, says that the Masterpiece case is "making a radical argument."

"When you look at it, they are saying there is a constitutional right, whether it's rooted in speech or religion, to discriminate," she said.

"A ruling for the bakery would have implications far beyond LGBT people and would put in jeopardy our longstanding laws against discrimination," she said.

But for Phillips, the argument is about artistic freedom under the First Amendment. He says he declined to create the cake because of the message it would have communicated, not because of the sexual orientation of the couple.

"Homosexual men are always, always, always welcome in my shop -- it has nothing to do with their orientation," he said. "There are just events that I cannot create cakes for. ... I cannot create cakes to help celebrate things that go against my core faith."

It's an argument that Obergefell is not buying. He sees the case as a "full-frontal assault" on the right to marriage.

"Not that they'd use this to rescind the right to marry," Obergefell said, "but they are using it to reinforce their belief to say in law and in practice, that my right to marry is not as valid as someone else's right to marry."

The case will be heard sometime this fall.