Light the match, put it to the rhyme book, make sure it all fits in the urn
The cream of life, beats and rhymes are butter
That in which I churn
All four lines (which includes the line that precedes those being annotated) are all inter-linked by life, death, food/money and fire/rebirth.
The burning rhyme book fits in the urn (which allows him to earn). This is the cream of life i.e. how he makes money (Wu-tang reference) but is also a reference to being cremated — therefore the ashes are the cream of life. He then inter-links cream to butter (butter-cream is a well known form of icing) which is how he flows on beats to make money as he churns out pristine lyricism.
These are probably the most clever set of metaphors you will ever hear in your fucking life.
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