All sin is equally wrong, but not all sin is equally bad. Acts are either right or wrong, either consonant with God’s will or not. But among good acts some are better than others, and among wrong acts some worse than others. Christians believe that thinking deliciously about adultery is just as wrong as committing it and not a different offense in kind. But Christians also know that adultery in one’s heart damages others less, at least for the short term, than does adultery in a motel room and may therefore rank as less serious on the badness spectrum.

   Similarly for other offenses: given a choice, our neighbor would rather have us covet her house than steal it. Neglecting to feed one’s children seems clearly worse than neglecting to expose them to the fine arts (though that is bad enough). The badness or seriousness of sin depends to some degree on the amount and kind of damage it inflicts, including damage to the sinner, and to some degree on the personal investment and motive of the sinner. 

Not the Way It's Supposed to Be: A Breviary of Sin - Cornelius Plantinga Jr.