This is a lesson on how deliberate venial sins can and do sometimes progress into the greatest of evils. Wanting what he could not have Ahab becomes angry and bitter. His contempt overflows into dialogue with his wife. His wife, perhaps in a bid to win Ahab's affection or to prove her power or worth, writes letters of deception in his name to have Naboth murdered. Who knows where this campaign of sin ultimately ended.
Thus is deliberate venial sin shown to be a seed planted in fertile soil, watered and germinated. How hard it can be to stop its growth when we consider it benign and leave it to itself. It's effect spreads, often unseen, until that point where its roots are well-established and deep. It is not without reason, therefore, that the Saints are unanimous in their conviction that the first step of the spiritual life is to abhor and flee deliberate venial sin. May God grant us the grace of a deeper conversion.