Like let's dress up the outside make it look nice and neat
But it's funny that's what they use to do to mummies while the corpse rots underneath
This is a reference to Jesus' rebuke to the religious rulers of his time in Matthew 23:27-28, which reads in the NIV as follows:
27 “Woe to you, teachers of the law and Pharisees, you hypocrites! You are like whitewashed tombs, which look beautiful on the outside but on the inside are full of the bones of the dead and everything unclean. 28 In the same way, on the outside you appear to people as righteous but on the inside you are full of hypocrisy and wickedness.
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