Hillary Clinton (Photo: CNN)

WASHINGTON (CNN) -- During a testy interview with NPR on Thursday, Hillary Clinton stood behind her role as secretary of state and her upbringing as a way to defend the fact that she was not publicly supportive of same-sex marriage until 2013.

NPR's Terry Gross pressed Clinton about her decision to come out in favor of marriage equality, leading the former secretary of state to give some of her fullest comments on the subject since she announced her support just weeks after she left the State Department in 2013.

"I did not grow up even imagining gay marriage and I don't think you probably did either," Clinton told Gross. "This was an incredibly new and important idea that people on the front lines of the gay rights movement began to talk about and slowly but surely convinced others of the rightness of that position. And when I was ready to say what I said, I said it."

Clinton, who said she has "evolved" on the issue, criticized those who "are never open to new information and they like to operate in a evidence free zone."

"One of my big problems right now is too many people think they have a direct line to the divine and they never want to change their mind about anything..." Clinton said. "I think it is good if people continue to change."

Clinton made a similar "direct line to the divine" comment as a way to knock people who are unwilling to change at an event on Wednesday in Chicago.

After a handful of questions on the topic, Gross said she was just trying to "clarify" whether Clinton had changed her opinion on the matter or whether the political winds on the issue had shifted, allowing Democrats' 2016 presidential frontrunner to come out in favor of same-sex marriage.

The question clearly irked Clinton, who said, "No, I don't think you are trying to clarify."

"I think you are trying to say that I used to be opposed and now I am in favor and I did it for political reason and that is just flat wrong," Clinton said. "So let me just state what I feel like you are implying and repudiate it. I have a strong record. I have a great commitment to this issue and I am proud what I have done and the progress we are making."

Gross then apologized, saying instead that maybe Clinton "really believed this all along," but "felt for political reasons, America wasn't ready yet."

At one point during the interview, Clinton stood behind her position as America's top diplomat - one she said was "out of domestic politics" - to defend the fact that she didn't come out earlier.

After leaving the State Department, she said, "I was able to very quickly announce that I was fully in support of gay marriage and it is now continuing to proceed state by state."

When Clinton came out in favor of same-sex marriage in 2013, she was one of many Democratic politicians to do so. Clinton's support came after both President and Vice President Biden backed gay marriage during the 2012 presidential race.

While at State, though, Clinton did make changes to help lesbian, gay, bisexual and transgendered people who work at in the department, including adding gender identity to the State Department's equal employment opportunity policy.

In her new memoir, "Hard Choices," Clinton writes about her those actions.

"When I look back at my time as Secretary, I'm proud of the work we did to extend the circle of human dignity and human rights to include people historically excluded," she writes. In particular, she notes she decided in 2009 to extend the "full range of legally available benefits and allowances to same-sex domestic partners of Foreign Service staff serving abroad."

Gross also pressed the former first lady on President Bill Clinton's signing of the Defense of Marriage Act, a federal law in which a key provision was struck down by the Supreme Court in June 2013. President Clinton signed the act into law in 1996, but before the case went to the nation's highest court, he urged the nine justices to rule it unconstitutional.

Asked whether she was happy that the key part of a law denying to legally married same-sex couples the same federal benefits provided to heterosexual spouses, Hillary Clinton said "of course," but then went on to defend the reasons her husband signed the law in the first place.

"Again, we are living at a time when this extraordinary change is occurring and I am proud of our country," Clinton said. "I am proud of the people who have been on the front lines of advocacy but in 1993, that was not the case and there was a very concerted effort in the congress to make it even more difficult and greater discrimination."