The back is what I said
Ready for the front, I rap it out the back of my head
Know it like the back of my hand
When Lupe says he is “ready for the front”, he’s saying that he has been in the background of rap for long enough. It’s time for him to jump to the front of the line and have everyone’s attention, the underground, and the really mainstream, that’s just how good he is.
“Ready for the front” = ready for battle. Ready to stand for what he thinks is right and against what he thinks is wrong — both in the current rap scene and the world in general.
“I rap it out the back of my head, Know it like the back of my hand”, Lupe is saying that his lyricism is so ingrained (at the back of the mind) into his brain that he can create deep and meaningful lyrics with ease. But although it’s in the back of his head, he knows all about making meaningful lyrics, similarly to the way you know everything about the back of your hand, it’s just natural.
“I rap it out the back of my head” can also refer to the opposing information centers in the brain. The frontal Lobe is responsible for decision making and impulse control (as well as housing much of long term memory) while the occipital lobe is responsible for vision. Lu can use different parts of his brain to draw from experience as well as to create something that’s never existed until now.
This also ties into an earlier line.
Here, Lupe is commenting on how other rappers are just now finally receiving the message that he “faxed” them from these previous lines. This connects with the next line “you ain’t seein what I said” describing how his competition took this long to realize his complex lyrics (they must be working with a slow fax machine).
He challenges them now by asking if they are ready for “the front” as in his full frontal assault. Lupe demonstrates his skill by showing his ability to rap “out the back of his head” connecting raps in the back of his memory that he has said in the past to raps that he is spitting in the present, like he does here. For this reason lupe is not worried about the competition of other rappers, because he is always a step ahead of his competitors. He warns other rappers a couple lines later from now on “gotta watch what I say”
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