Understanding Sexual Sin: The Harvest USA Tree Model

The following blog is an article from our 2021 Harvest USA Magazine entitled Standing Firm for His Glory. To read more articles from this issue, simply click here or visit www.harvestusa.org/magazines/.

“But isn’t it just a lust problem?” Mike asked. I was explaining to Mike the Harvest USA Tree Model, the core content of our ministry to both individuals and churches. Mike wanted to believe what I was saying about the deeper aspects of his sin. It gave him hope that there was a path to victory in his fight against the porn habit he’d been losing for years, because willpower certainly hadn’t worked. His objection revealed a problem that most of us encounter when thinking about our sin.

Mike’s question forces us to seek a more complete understanding of sin. We tend to think of sin in simple ways that only scratch the surface: I’m tempted; I fall; I repeat. But a biblical view of sin goes much deeper. This is what our Harvest USA Tree Model illustrates.

Jesus describes sin as having a source deep within us, in the heart, the epicenter of where our intellect, will, and affections all converge. In Matthew 15:18–19, Jesus said, “But what comes out of the mouth proceeds from the heart, and this defiles a person. For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.” Thinking of our hearts as part of a tree originates from Jesus’ words in Luke 6:43–45: “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 thornbushes, 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 heart produces evil, for out of the abundance of the heart his mouth speaks.” Building upon these verses, our Tree Model pictures the heart as the source of a tree, the seed.

The Seed: Our Hearts

The most basic characteristic of the seed, or heart, is that it is fallen. The word “autonomy” summarizes the sinful inclination of our hearts. We desire self-rule rather than being ruled by the authority and care of God. Our desire for autonomous independence from God affects every aspect of our lives. It shapes our reactions to our circumstances and experiences; it skews our deepest desires; it taints our functional worldviews. These are the inner workings of sin that bear fruit in what we do. The following three make up the other elements of the tree: the soil, the roots, and the trunk.

The Soil: Our Circumstances and Experiences

The soil is the context for the seed. The parents to whom we were born, our families, and our peers are all part of the soil. It is all the things those people do to us or for us—or neglect to do. It is everything that happens to us, good or bad. We are praised, abused, affirmed, attacked, protected, or wounded. We experience trauma and suffering, or we live in shelter and safety. Together, these experiences comprise the context in which our fallen hearts are active.

It is important to note that the soil is influential but not determinative. The influence of experience and context can be profound and must be taken into account if we want to understand and turn from entrenched sin patterns, but our circumstances do not determine our actions. Our fallen hearts are always interacting with the soil, interpreting and responding to both positive and negative experiences.

The Roots: Our Deepest Desires

One of the ways in which our hearts interact with our contexts is by desire. We were created to receive certain blessings and gifts from the gracious hand of our Creator. As his image bearers, God gave us desires for security, significance, glory, affirmation, love, purpose, and order. Marriage, fellowship, friendship, and other social connections were intended to be conduits of love, affirmation, affection, and intimacy as we became “fruitful and multiplied,” according to God’s blessing.

We still want all of these blessings that were given or promised to us, but now our hearts want them autonomously. We don’t want to receive God’s blessings in his way, in his time, according to his authority or design; we want them on our terms. Second, the soil itself is cursed, and the world and the relationships in it are broken. This combination means that our desires are problematic for us. Separated from God, the true source of every blessing we could rightly desire, we tend to substitute counterfeits to suit our fallen hearts. These counterfeits become our idols. When we speak of idols of the heart, we are referring to desires that have become so important to us that they have replaced God in our hearts. They control us, so we sometimes refer to these as controlling desires.

The Trunk: Our Functional Worldviews

Our idolatrous desires both shape and are shaped by our thinking. We develop patterns of thought that form the grid for our interactions with our world. We sometimes call these “shoots” because they arise out of our hearts’ interaction with the soil, but, because they continue to grow until they are strong and fixed, we can also call this the trunk. Both terms refer to our functional worldviews—our unspoken and largely unconscious set of beliefs about God, the world, ourselves, and other people, which form the basis for our daily lives. These are not the doctrinal affirmations you would likely recite if asked to describe what you officially believe. Instead, this set of beliefs is reflected in the ways that you actually live.

The Gospel: New Hearts, New Trees

The Tree Model illustrates that our behaviors—the fruit—are but a symptom of how the tree is functioning. When you hope in Christ, he renews your heart, and your entire tree is renewed. The Bible promises us a new heart (Ezekiel 36:26–27) and describes and our new life as being “in Christ” (Romans 8:1), “hidden with Christ” (Colossians 3:3), and—using a tree metaphor—“grafted into” the tree of salvation (Romans 11:17). The new heart and new life that Christ gives is the beginning of an entirely new tree. In the gospel, our true and eternal identity is in Christ, even though we still battle with the patterns and baggage of our old ways. Rather than simple self-discipline and willpower, though, the real source of change is new faith and affections in our hearts, redeemed desires, and transformed worldviews—all given to us in Christ.

Back to Mike

So how did this help Mike, the questioning struggler with whom I was speaking? By examining his soil, Mike identified a few influential experiences: His dad abandoned the family when he was nine, and his mom became an alcoholic, leaving Mike to care for three younger siblings. By outward appearances, he succeeded admirably in this role, proving himself capable and receiving praise from others, but Mike’s heart became controlled by a fear of chaos and a strong desire for both control and affirmation—his roots. He developed the unspoken belief that, on one hand, people were a threat to him; on the other hand, their adoration of him was essential to his worth. He believed he must control people and things at all costs. Pornography was the fruit. In it, he fantasized about the adoration he craved while holding complete control and avoiding the chaos and threat of relationships. Now, no longer autonomous but armed with faith that his heart and identity were new in Christ, Mike brought all the truths and promises of the gospel to his experiences (soil), his desires (roots), and his thoughts (trunk).

Of course, this is a simplified and condensed version of Mike’s story. In reality, change happens over a lifetime of discipleship, in relationship with others in the Body of Christ. This is why we want leaders and individuals in churches to have this tool. We use our Tree Model to train people in a biblical view of sin and the gospel.

 

About The Author
Jim Weidenaar joined the Harvest USA staff in June of 2012 as Director of Church Equipping and the Greater Pittsburgh Region (GPR). He has a burden to help those struggling with sexual sin, that they will come to understand and experience progress in gospel repentance. Jim has a Masters Degree in Theological Studies (MTS) from Calvin Theological Seminary, Grand Rapids, MI, and a Doctorate in Historical and Theological Studies (PhD) from Westminster Theological Seminary, Glenside, PA. He resides in the eastern suburbs of Pittsburgh with his wife and daughter.

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