You know I got two belts, the black and the white one
I begin and I master
In the martial arts, the color of one’s belt indicates how far one has progressed in the discipline. The white belt indicates someone who has begun to learn the style, and the black belt indicates someone who has mastered the art
As a trained karate expert (who got his black belt at age 11!), Lupe understands that — objectively-speaking — he is one of the masters of all rap, he nevertheless acknowledges that he has much more to learn..
“I master” could also be a reference to chain Eyemasters, where you can buy eye glasses, which Lupe wears (as noted in the next line)
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