Brittany Brees penned a lengthy statement on social media over the weekend ... saying she and the NFL star didn't realize how their personal opinions about the flag affected others.

"WE ARE THE PROBLEM," Brittany said ... "Only until the last few days, until we experienced the death threats, we experienced the hate … Did I realize that these words were speaking directly to us."

Unclear if any of the threats were deemed serious by law enforcement. We're working on it.

Brittany continued ... explaining, "To say 'I don’t agree with disrespecting the flag' I now understand was also saying I don’t understand what the problem really is."

"I don’t understand what you’re fighting for, and I’m not willing to hear you because of our preconceived notions of what that flag means to us."

"That’s the problem we are not listening, white America is not hearing. We’re not actively LOOKING for racial prejudice."

Brittany insists she and Drew don't "have a racist bone in our body" ... and now, she's pledging to do more to help the black community in their fight for social justice.

"Somehow we as white America, we can feel good about not being racist, feel good about loving one an another as God loves us," Brittany said. "We can feel good about educating our children about the horrors of slavery and history."

"We can read books to our children about Martin Luther King, Malcolm X., Hank Aaron, Barack Obama, Rosa Parks, Harriet Tubman and feel like we are doing our part to raise our children to love, be unbiased and with no prejudice. To teach them about all of the African Americans that have fought for and risked their lives against racial injustice. Somehow as white Americans, we feel like that checks the box of doing the right thing. Not until this week did Drew and I realize THAT THIS IS THE PROBLEM."

She continued, "To all of our friends and anyone we hurt we will do better ... We are sorry."