Kevin DeYoung (in The Hole in our Holiness) discusses the crucial importance of recognizing that some sins are more sinful than other sins:
As R. C. Sproul puts it, “The idea of gradation of sin is important for us to keep in mind so we understand the difference between sin and gross sin.” All our sins are offensive to God and require forgiveness.
But over and over the Bible teaches that some sins are worse than others.
The Mosaic legislation prescribes different penalties for different infractions and requires different sacrifices and payments to make restitution.
Numbers 15 recognizes the difference between unintentional sins and those done “with a high hand” (Num. 15:29–30).
Here’s the problem: when every sin is seen as the same, we are less likely to fight any sins at all. Why should I stop sleeping with my girlfriend when there will still be lust in my heart?
Why pursue holiness when even one sin in my life means I’m Osama bin Hitler in God’s eyes? Again, it seems humble to act as if no sin is worse than another, but we lose the impetus for striving and the ability to hold each other accountable when we tumble down the slip-n-slide of moral equivalence.
All of a sudden the elder who battles the temptation to take a second look at the racy section of the Lands’ End catalog shouldn’t dare exercise church discipline on the young man fornicating with reckless abandon. When we can no longer see the different gradations among sins and sinners and sinful nations, we have not succeeded in respecting our own badness; we’ve cheapened God’s goodness.
If our own legal system does not treat all infractions in the same way, surely God knows that some sins are more heinous than others. If we can spot the difference, we’ll be especially eager to put to death those sins which are most offensive to God.
DeYoung, Kevin (2012-08-07). The Hole in Our Holiness: Filling the Gap between Gospel Passion and the Pursuit of Godliness (Kindle Locations 1060-1066). Good News Publishers. Kindle Edition.