"Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness." (Matthew 23:27)
"Beauty is only skin deep" seems to be the modern secular equivalent of this "woe" in Matthew 23. The corresponding Old Testament statement is probably this: "As a jewel of gold in a swine's snout, so is a fair woman which is without discretion" (Proverbs 11:22). This principle has lasted for millennia simply because it is easily observed in all cultures. Our Lord's application to the scribes and Pharisees was particularly pointed: "Even so ye also outwardly appear righteous unto men, but within ye are full of hypocrisy and iniquity" (Matthew 23:28). God is not interested in the "pretty outside" but in what's on the inside. "But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the LORD seeth not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart" (1 Samuel 16:7).
Hypocrisy and iniquity are the two attributes of "uncleanness" identified by Christ. The core of hypocrisy is the intent to deceive others, either with actions or words. And the core of the biblical teaching about deception is the false teacher--those who look like and talk like God's people, "but inwardly they are ravening wolves" (Matthew 7:15). Iniquity is the biblical term for "without law." Such a person has no desire to submit to authority, and is both willing to do evil and is dangerous to be around. Cain murdered Abel, the Bible insists, "because his own works were evil, and his brother's righteous" (1 John 3:12).
Such a condition should never plague us. Jesus "gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works" (Titus 2:14). HMM III