Bad Meets Evil - Lighters Lyrics Meaning

Eminem's part is a message to the people who doubted he could keep his game tight, now that he's clean. That it was a struggle at first("it wasn’t that long ago when Marshall sat, luster lacked, flustered
Cuz he couldn’t cut mustard, muster up nothing") but that he will always rise to the top ("By the time you hear this I will have already spiraled up I would never do nothing to let you cowards fuck my world up"). It means to much to him ("This rap game’s nipple is mine for the milking,
Till nobody else even fucking feels me, till’ it kills me I swear to god I’ll be the fucking illest in this music There is or there ever will be")

What I get from Royce's part is that he's grateful to Eminem ("To tell Shady I love him the same way that he did Dr Dre on the Chronic Tell him how real he is or how high I am Or how I would kill for him for him to know it")for giving him the chance that no-one else did ("I remember when T-Pain aint wanna work with me")
I'm not sure on the rest, I'm not familiar with his story