How do I know when my actions are a result of sin in my heart or because of bodily weakness?

This is an important question because it rightly recognizes that we humans are body-soul beings. We are physically embodied, spiritual beings, and both aspects of our personhood matter in our day-to-day lives. The most accurate way to conceive of our human makeup is that we are constituted as a duality—body and soul. The Bible uses terms like soul, spirit, and heart interchangeably to refer to the immaterial aspect of our personhood. But how should we understand the relationship between the immaterial and material aspects of our personhood, and how might that help us answer the question regarding sin?

Most often, Scripture highlights the psychosomatic unity of the person. Both body and spirit are necessary for normal human existence. My body doesn't go to the post office. I go to the post office. My spirit doesn't read Scripture. I read Scripture. So there's unity there.

But the Bible also makes distinctions between the two. Scripture views our hearts as the moral center of our lives from which flow our thoughts, affections, desires, motives, and actions. The Bible doesn't view our bodies in these moral categories, but rather uses categories of weakness, strength, finitude, limitation, or difference. One of the places where we see this distinction with regard to the origin of sin is in Luke 6:43–45, where Jesus says, "For no good tree bears bad fruit, nor again does a bad tree bear good fruit, for each tree is known by its own fruit. For figs are not gathered from thorn bushes, nor are grapes picked from a bramble bush. The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart, his mouth speaks.”

Sin arises out of the heart. Scripture nowhere says that sin originates in the body or that the body can be the initiator of moral action. That seems to be the exclusive domain of the heart. Our bodies can be diseased or disabled, but they are not the source of sin. That said, significant bodily weakness or limitation may lower the threshold for sin. Our bodies can impact our agency and ability. Another way to say this is that the body affects the heart for better or for worse. I'll give some examples. Why do we use the word hangry? It's a recognition of the fact that when we are hungry, we are prone to irritation, whether we're children or adults. It's not that our empty stomach somehow force the lever of our hearts to grumble and complain and be short with someone, but our hunger does create a bodily context that may make it harder to be kind or patient.

Similarly, we see this with the effects of insomnia. It's not that we automatically become nasty when we have interrupted and poor sleep, but there's no doubt that it may be harder to be attentive and loving to those around you if you're sleep deprived. There is an extra pressure on us when faced with this bodily weakness. In more severe situations, traumatic brain injury or stroke for example, the limitations of the body take more of a center stage, impacting to a greater extent our agency and ability. Problems with impulse control, anger, and poor judgment may show up for the first time in a sufferer's life.

Now, what are some implications of this, if you will, brief tour of biblical anthropology? Our hearts are always active. Every person is responsive to God and responsible for their actions as image-bearing worshippers. When we commit sins of omission or commission, we ask for forgiveness from God and from those we have hurt. For those in Jesus Christ, transformation into the character of Christ is not prohibited by their physical constitution. As Ed Welch says, the body cannot keep us from spiritual growth. Paul highlights this in 2 Corinthians 4:16: "So we do not lose heart. Though our outer self is wasting away, our inner self is being renewed day by day.” And that's good news.

However, we cannot ignore the very real and powerful influences that bodily limitations place upon a person. To be sure, every person with their particular constellation of strengths and weaknesses is called to love God and neighbor, but the shape of that love may look different when a person's health is compromised. This should not surprise us. We naturally shift our expectations for our children's obedience based on their age and developmental level. While all children are called to honor their father and mother, the specific expectations for obedience look different for a four-year-old versus a sixteen-year-old. If we make adjustments in the normal development of children, should we not show compassion and understanding and patience for those whose bodily suffering puts pressure on their inner man?

We want to avoid the extremes when thinking about bodily weakness and sin: “Either my body made me sin” or “My body doesn't matter.” I hope you've seen that Scripture gives us a much more balanced way forward.