He’s not a demon but he did arise from the underground in the form of a rose in cement (something like a diamond in dirt).
There are several nuances in this line:
cement : Concrete is a characteristic feature of the ghettos and projects that are usually neglected by society. That is the cement hell that Jay came from. Additionally, the cement is like the surface that sits on top of this large hidden world of the streets. Jay Z grew like a plant and rose through this world till his ‘flower’ breached the surface and blossomed for everyone to see.
This line is basically describing his transition from the underground to the mainstream. Hence the play on the devil.
a rose : Wordplay. Jay Z arose from the depths of hell.
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