Skylar Grey didn't write the hook with herself in mind as a vocalist. She explained to Billboard
"I was thinking, you know, 'this is kind of gospel-sounding, it'd be dope to have like a gospel singer on it,' and I kind of wrote a little bit out of my range vocally. But it was just funny because a month later [Macklemore] hit me up and was like, 'I want you to stay on the song.' They liked the fact that my voice wasn't gospel, so it made it less expected with that type of melody, I guess. So I ended up staying on the song, and I had to practice a lot, playing it, to be able to perform it live - but I figured out how to do it.
It's very rare that I write something thinking somebody else is going to be on it, and then I end up on it. Usually it's kind of the opposite, I write a song and I think I'm gonna sing it, and then somebody else takes it from me [Laughs]."