And even if Jehovah witness, bet he'll never testify, D'evils
This refers to the practice of killing a witness to a crime before that witness can testify against you. Jay claims that even if a god like Yahweh, who is supposed to have the highest morality in the universe witnessed this crime, Jay-Z would be able to intimidate Him into silence (note the play on the name of the Jehovah’s Witness religion).
Since one of Jay’s nicknames is Jayhova, this could be him referring to himself in the third person and claiming that even if he saw someone else commit a crime, he would never snitch.
Jay-Z in Decoded explains this line saying:
The song ends with a dizzying carousel of conversations: First the narrator address his mother, then his girl (“boo), and finally a last victim. The narrator is completely lost to the "D'Evils.” He taunts his victims, defends himself, brags about how low he gets down, invites niggas to try to come get him like George Bush saying “bring ‘em on” to the terrorists. The final two lines, contrasting the demons in his head with a God he thinks is powerless, show how deeply he’s fallen into a moral vacuum. The song isn’t about literal demonic possession, of course, even if some sloppy listeners claim that it is; the truth is you don’t need some external demon to take control of you to turn you into a raging, money-obesessed sociopath, you only need to let loose the demons you already have inside of you.
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