I found this post on RecoverTheGospel.com. It's a section out of Thomas Watson's book, The Godly Mans Picture:

A reproof to such as are only PRETENDERS to Godliness

“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 dead men’s bones and everything unclean. In the same way, on the outside you appear to people as righteous but on the inside you are full of hypocrisy and wickedness.” Matthew 23:27-28

Here is a sharp rebuke to such as are “glittering dross” Christians, who only make a show of godliness, like Michal, who put “an image in the bed”, and so deceived Saul’s messengers (1 Sam. 19:16). These our Savior calls “whited sepulchers” (Matt. 23:27)—their beauty is all paint! In ancient times a third part of the inhabitants of England were called Picts, which signifies “painted”. It is to be feared that they still retain their old name. How many are painted over with a religious profession, whose seeming luster dazzles the eyes of beholders—but within there is nothing but putrefaction! Hypocrites are like the swan, which has white feathers—but a black skin; or like that flower, which has a lovely appearance—but a bad scent. “You have a name that you live, and are dead” (Rev. 3:1). These the apostle Jude compares to “clouds without water” (Jude 12). They claim to be full of the Spirit—but they are empty clouds; their goodness is but a religious cheat.

Question: But why do people content themselves with a show of godliness?

Answer: This helps to keep up their fame. Men are ambitious of credit, and wish to gain repute in the world, therefore they will dress themselves in the garb and mode of religion, so that others may write them down for saints. But alas, what is one the better for having others commend him—and his conscience condemn him? What good will it do a man when he is in hell—that others think he has gone to heaven? Oh, beware of this! Counterfeit piety is double iniquity.

1. To have only a show of godliness is a God-enraging sin

The man who is a pretender to saintship—but whose heart tells him he has nothing but the name, carries Christ in his Bible but not in his heart. Some political design spurs him on in the ways of God; he makes religion a lackey to his carnal interest. What is this but to abuse God to his face, and to serve the devil in Christ’s livery? Hypocrisy makes the fury rise up in God’s face; therefore he calls such people “the generation of his wrath” (Isaiah 10:6). God will send them to hell, to do penance for their hypocrisy!

2. To make only a show of godliness is self-delusion

It is a horrible mistake to take a show of grace, for grace. This is to cheat yourself: “deceiving your own souls” (Jas. 1:22). He who has counterfeit gold instead of true gold, wrongs himself most. The hypocrite deceives others while he lives—but deceives himself when he dies.

3. To have only a name, and make a show of godliness, is odious to God and man

The hypocrite is abhorred by all. Wicked men hate him because he makes a show, and God hates him because he only makes a show. The wicked hate him because he has so much as a mask of godliness, and God hates him because he has no more. “You have almost persuaded me to be a Christian” (Acts 26:28). The wicked hate the hypocrite because he is almost a Christian, and God hates him because he is only almost one.

4. To make a show of piety is a vain thing

Hypocrites lose all they have done. Their sham tears drop beside God’s bottle; their prayers and fasts prove abortive. “When you fasted and mourned, did you at all fast unto me, even to me?” (Zech. 7:5). As God will not recompense a slothful servant, neither will he recompense a treacherous one. The hypocrites’ full reward is in this life: “They have their reward” (Matt. 6:5). A poor reward—the empty breath of men. The hypocrite may make his receipt and write, “Received in full payment”. Hypocrites may have the praise of men—but though these triumphs are granted them, they shall never have the privilege of sitting in heaven. What acceptance can he look for from God, whose heart tells him he is no better than a charlatan in divinity?

5. To have only a pretense of godliness will yield no comfort at death

Will painted gold enrich a man? Will painted wine refresh him who is thirsty? Will the paint of godliness stand you in any stead? How were the foolish virgins better for their “blazing lamps”, when they had no oil? What is the lamp of profession without the oil of grace? He who has only a painted holiness shall have only a painted happiness.

6. You who have nothing but a specious pretext and mask of piety expose yourself to Satan’s scorn

You shall be brought forth at the last day, as was Samson, to make the devil sport (Judges 16:25). He will say, “What has become of your vows, tears, confessions? Has all your religion come to this? Did you so often defy the devil, and have you now come to dwell with me? Could you meet with no weapon to kill you—but what was made of gospel metal? Could you not suck poison anywhere but out of ordinances? Could you find no way to hell—but by counterfeit godliness?” What a vexation this will be, to have the devil thus reproach a man! What will it be to have the devil triumph over a man at the last day!

Let us therefore take heed of this pious pageantry or devout stage-play. That which may make us fear our hearts the more is when we see tall cedars in the church worm-eaten with hypocrisy. Balaam a prophet, Jehu a king, Judas an apostle—all of them stand to this day on record as hypocrites.

It is true that there are the seeds of this sin in the best Christian; but as it was with leprosy under the law, all who had swellings or spots in the skin of the flesh were not reputed unclean and put out of the camp (Lev. 13:6); so all who have the swellings of hypocrisy in them are not to be judged hypocrites, for these may be the spots of God’s children (Deut. 32:5). But that which distinguishes a hypocrite is when hypocrisy is predominant and is like a spreading cancer in the body.

Question: When is a man under the dominion and power of hypocrisy?

Answer: There are two signs of its predominance:

(i) When one serves God for sinister ends.

(ii) When there is some sin dear to a man, which he cannot part with. These two are as clear signs of a hypocrite as any I know.

Oh, let us take David’s candle and lantern, and search for this leaven, and burn it before the Lord!

Christian, if you mourn for hypocrisy—yet find this sin so potent that you cannot get the mastery of it, go to Christ. Beg of him that he would exercise his kingly office in your soul, that he would subdue this sin, and put it under the yoke. Beg of Christ to exercise his spiritual surgery upon you. Desire him to lance your heart and cut out the rotten flesh, and that he would apply the medicine of his blood to heal you of your hypocrisy. Say that prayer of David often: “Let my heart be sound in your statutes” (Psalm 119:80). “Lord, let me be anything rather than a hypocrite.” A double-heart will exclude from one heaven.