R.C. Sproul on Legalism

"Perhaps the most deadly and widespread form of legalism is that type which adds legislation to the law of God and treats the addition as if it were divine law. The Old Testament prophets expressed God's fury at this form of behavior, lamenting the result of "binding men where God had left them free." It is a manifestation of man's fallenness to impose his own sense of propriety on other people, seeking mass conformity to his own preferences and adding insult to it by declaring these prejudices and preferences to be nothing less than the will of God. A frequent point of conflict between Jesus and the Pharisees centered on the Pharisees' traditions, which imposed hardships on the people who were bound by these man-made obligations. Jesus rebuked the Pharisees because they had elevated their traditions to the level of the law of God, seeking not only to usurp God's authority, but to oppress mankind.

"The elevation of human preferences to the level of divine mandate is not limited to an isolated group of moralistic Pharisees in the first century. The problem has beset the church throughout its history. Not only do traditions develop that are added to the law of God, but in many cases they become the supreme tests of the faith, the litmus test by which people are judged to be either Christians or non-Christians. It is unthinkable in the New Testament that a person's Christian commitment would ever be determined by whether or not that person engaged in dancing, or in wearing of lipstick and the like. Unfortunately, so often when these preferences become tests of faith, they involve not only the elevation of nonbiblical mandates to the level of the will of God, but they represent the trivialization of righteousness. When these externals are elevated to the level of being measuring rods of righteousness, we begin to major in minors and obscure the real tests of righteousness." R.C. Sproul, Following Christ, (Wheaton, Illinois: Tyndale House Publishers, Inc., 1991), pp. 323-325.

"The manipulation of conscience can be a destructive force within the Christian community. Legalists are often masters of guilt manipulation, while antinomians master the art of quiet denial. The conscience is a delicate instrument that must be respected. One who seeks to influence the conscience of others carries a heavy responsibility to maintain the integrity of the other person's own personality as crafted by God. When we impose false guilt on others we paralyze our neighbors, binding them in chains where God has left them free. When we urge false innocence we contribute to their delinquency, exposing them to the judgment of God." R.C. Sproul, Following Christ, (Wheaton, Illinois: Tyndale House Publishers, Inc. 1991), p.390.

(taken from Patriarchy.org)