I flinch a little bit when you ask me that question because I have in my memory not so fond recollections of having answered that question in the past when people got very upset with what I said. What mystifies me is that it seems that there are a lot of Christians who hold the position that there are no gradations of sin, that all sin is sin and there's no difference between less serious or more serious sins.
The Roman Catholic Church historically makes a distinction between venial sin and mortal sin, meaning that some sins are more heinous than others. Mortal sin is so called because it's serious enough to destroy the saving grace in the soul. It kills grace, and that's why it's called mortal.
Protestant Reformers in the sixteenth century rejected the concept of the distinction between venial and mortal. Calvin, for example, said that all sin is mortal in the sense that it deserves death, but no sin is mortal, save the blasphemy of the Holy Spirit, insofar as it would destroy the salvation that Christ has achieved for us. In the Protestant reaction to the Roman Catholic distinction between venial and mortal sin, the Protestant Reformers did not deny gradations of sin. They still maintained a view of lesser and greater degrees of sin. What I'm saying is that in orthodox Christianity, both Roman Catholic and Protestant denominations have taken the position that there are some sins that are worse than other sins. They make these distinctions because it's so plainly taught in the Scriptures.
If we look at the Old Testament law, we see that certain offenses are to be dealt with in this world through capital punishment and others through corporal punishment. Distinctions are made, for example, between murder with malice aforethought and what we would call involuntary manslaughter. There are at least twenty-five occasions where the New Testament makes a distinction between lesser and greater forms of evil. Jesus says, for example, at his own trial, "Those who have delivered me to you have greater guilt than you have."
There is abundant evidence in the Scriptures to postulate a view of the gradations of sin. Not only that, but the very simple principles of justice would indicate that. But I think that people stumble on this point for two reasons. One is Saint James's statement "He who sins against one point of the law, sins against the whole law." That sounds as if James is saying that if you tell a little white lie, it's as bad
as killing somebody in cold blood. But James is actually saying that all sin is serious insofar as every sin is an offense against the lawgiver, so that in the slightest sin I'm sinning against the law of God. I have
violated the whole context of that law in many ways. So all sin is serious, but it doesn't follow logically that all sin is equally serious.
People also refer to Jesus' statement that if you lust after a woman, you've violated the law against adultery. Jesus doesn't say that it is as bad to lust as it is to commit the actual act. He's simply saying that if you merely refrain from the actual act you're not totally clean; there are lesser elements of the law that you have violated.
~ RC Sproul, Now - That's a Good Question!