Historically speaking, both Roman Catholicism and Protestantism have understood that there are degrees of sin. The Roman Catholic church makes a distinction between mortal and venial sin. The point of that distinction is that there are some sins so gross, heinous, and serious that the actual commission of those sins is mortal in the sense that it kills the grace of justification that resides in the soul of the believer. In their theology, not every sin is devastating to that degree. There are some real sins that are venial sins. These are less serious sins in terms of their consequences, but they don’t have the justification-killing capacity that mortal sins have.
Many evangelical Protestants have rejected the idea of degrees of sin because they know that the Protestant Reformation rejected the Roman Catholic distinction between mortal and venial sins. As a result, they’ve jumped to the conclusion that there are no distinctions between sins in Protestantism.
We should return to the views of the Reformers themselves. John Calvin was an outspoken critic of the Roman Catholic Church and their distinction between mortal and venial sin. Calvin said that all sin is mortal in the sense that it deserves death. The book of James reminds us, “For whoever keeps the whole law but fails in one point has become accountable for all of it” (James 2:10). Even the slightest sin is an act of cosmic treason. We fail to feel the gravity of our actions to this degree, but it is true.