I shouldn't have to rhyme these words
In the rhythm for you to know it's a rap

from Eminem – Not Afraid Lyrics on Rap Genius

Meaning

Here, Em goes off the beat and then rhymes about going off the beat. This kind of meta-rhyme stuff is a little inside baseball, but it’s a big part of why Em’s one of the most technically-gifted emcees in mainstream rap

There’s also an “it’s a wrap” pun here: he shouldn’t have to be spitting this rhyme for you to know that Em’s victory in any challenge to Em’s dominance is a foregone conclusion

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