"Hey guys ... I wanted to do SOMETHING for the victims' families and I didn't really know what else to do," he tweeted. "Writing songs is pretty much the only thing I'm good at so I hope you'll share this as you see fit ... Today makes no sense ... God has blessed me with this gift and it felt wrong not to share it. I hope this song finds its way to proper ears."
The gently strummed acoustic song opens with the lines, "Today we shed our tear for you/ Tomorrow we do it all again/ They say that time will make it better/ I think about what could have been."
In light of the horror unleashed by gunman Adam Lanza on Friday in the small town, in which he gunned down 20 first-grade children and six adults, including his mother, Posner's song seeks some brightness in one of the darkest chapters in the nation's history.
"Still, I believe that there's a whole lot of good people/ I believe that there's a light," he sings in a high, clear voice. "And I believe in more than things I can see, my love/ And I know this isn't right/ But maybe this will make sense in heaven and I'll understand why you're gone ... maybe this will make sense in heaven/ Cuz right now it don't make sense at all."
The rapper included an Instagram message for the families of the victims as well, writing, "I hope this song will help just a tiny, tiny bit to ease the pain of your loss. Maybe this will make sense in heaven."
President Obama attended a prayer vigil for the families of those killed in the incident on Sunday night, speaking emotionally about the lives lost and the need to come together as a nation to prevent such future tragedies.
"We gather here in memory of twenty beautiful children and six remarkable adults," he said, at points appearing on the verge of tears. "They lost their lives in a school that could have been any school; in a quiet town full of good and decent people that could be any town in America ... Here in Newtown, I come to offer the love and prayers of a nation. I am very mindful that mere words cannot match the depths of your sorrow, nor can they heal your wounded hearts.
"I can only hope it helps for you to know that you're not alone in your grief; that our world too has been torn apart; that all across this land of ours, we have wept with you, we've pulled our children tight. And you must know that whatever measure of comfort we can provide, we will provide; whatever portion of sadness that we can share with you to ease this heavy load, we will gladly bear it. Newtown -- you are not alone."
At the end of his address, the president read the first names of the youngest victims, telling the audience, "God has called them home. For those of us who remain, let us find the strength to carry on, and make our country worthy of their memory."