The answer is: The heart

Matt 15:19; Mark 7:21

When we talk about sin, we should consider what it means to have a “heart.” In the biblical sense, “heart” doesn’t just refer to our emotions, but is also where our true character lies—our intentions, thoughts, and motivations. This understanding is important because it frames the root of sin as internal, rather than something external or forced upon us.

Matthew 15:19 and Mark 7:21 remind us that all sorts of negative actions originate from this inner part of us. Jesus highlighted that out of the heart come evil thoughts, murders, and various immoral behaviors. It’s like a wellspring; what bubbles up reflects what is already in our hearts. So the focus isn't solely on external actions but on a deeper, transformative journey to something greater.

Interestingly, the ancient Hebrew perspective also linked the heart with decision-making and judgment—essentially, how we live our lives originates internally. Moreover, woven through Bible references is the idea that redemption involves healing this heart, shifting frailties into strengths—think of verses such as Proverbs 4:23 which urges us to guard our hearts vigilantly.

You could say the Bible urges a change of heart; it promotes awareness of our thoughts and feelings in order to lead to righteous action. This journey involves reflection, humility, and ultimately, growth—symbolizing not just a deviation from sin, but embracing newfound pathways towards compassion and understanding. Seeking to change the heart invites a transformative quest that can bring out the very best in humanity.