The answer is: Anger

Matthew 5:21-22 - In the Sermon on the Mount, Jesus teaches that harbouring anger towards a brother or sister is equivalent to committing murder in one’s heart. This radical redefinition of sin emphasizes inner attitudes over actions, illustrating that true righteousness involves not just the avoidance of sin but also cultivating pure intentions.

In the heart of the Sermon on the Mount, Jesus reshapes our understanding of morality and ethics, elevating the conversation from mere external actions to the intricate workings of the heart. Did you know that this idea of a "holistic ethical life" is echoed in teachings from various philosophies and religions? Many cultures have debated the implications of anger and its capacity to ferment into more destructive behaviors.

When Jesus links anger to murder, He's not just making a provocative statement. He's encouraging a deep introspection, a self-reflection that can lead to profound transformation. Understanding this can shine a light on the human experience—how sometimes an impulsive thought, if unexamined, can spiral into gripping animosity.

Moreover, the Greek word for anger used in this passage, "orge," implies a deeper, simmering enmity, which is quite distinct from the transient frustration we all feel from time to time. Addressing this can help millions grapple with complex emotions and relational conflicts.

It's fascinating to note that tools and practices such as forgiveness and reconciliation celebrated in various humanistic frameworks resonate closely with this teaching. This ancient wisdom calls us to nurture empathy and kindness, confronting anger rather than letting it fester. So, next time our face flushes with anger, we might remember to pause, digging deeper into our hearts rather than letting destructive thoughts take root. Such mindfulness contributes not only to personal peace but also to brighter relationships with those around us.