Poison ivy leaves are a lot like bad spiritual fruit. Both are the result of a root from something bad. Poison ivy has seemingly endless yards of gnarly, woody roots beneath the surface, and every inch must be dug up to keep the ivy from returning. It’s also necessary to diligently search for evidence of the vine for months—and even years—thereafter, in case the tiniest trace remained and takes root again.
My husband dug out the root; he worked until the task was accomplished, to prevent future re-growth and resulting pain.
Our “bad” spiritual fruit, too, is the distasteful result of something with deep (often hidden) roots. And sometimes, we had nothing to do with how the seed got planted.
When someone sins against us, it wounds us, placing a vulnerable entry spot into our lives - a hole into our spiritual fortress, so to speak.
While our choice to quickly (and sometimes repeatedly) forgive (Matthew 6:14-15) can shore up these breaches to our defenses, often we are so conscious of our hurt that we focus on protecting ourselves from future hurt by every carnal (non-spiritual) means we can think of.
Maybe we devote our energy to making sure this person "pays" for his/her sin; maybe we want to wait till the perpetrator is "really sorry" for what he/she did before we forgive; or maybe we even think we've forgiven, but we've only said the words and buried the pain, rather than let God minister to our spirits and souls (emotions, thoughts and desires). However, if the entry point (wound) is left unprotected, that particular sin-seed will take root in that entry point-- sending the roots as deep as possible.
We didn't cause the vulnerable entry area, and we certainly didn't send the roots into that area. Sin did that.
BUT-- the fruit of the sin that was committed against us will come into our own lives if we don't allow God to heal the wound that was caused when a person hurt us through his or her sin.
Look at an example we all understand. A child who is abused didn't bring this violence into his/her own life, but unless he/she is healed and rid of it by the Holy Spirit and excellent counseling, he/she is likely to be angry, frustrated, and violent; and may even produce bad fruit by perpetuating this sin into the lives of others—namely his or her own children.