Jesus lists examples of the wickedness we can generate inside. What’s included? Slander is there, where we use the amazing power of words to dishonour other people unfairly to benefit ourselves. Arrogance is there, where we proudly think too highly of ourselves, demanding respect and putting ourselves above others. Folly is there, where we lack the judgement to live wisely and blindly make decisions which are stupid, dangerous and corrupt. Each evil is of ancient origin, having tracked humanity ever since we first rebelled against God. Each is unworthy of God who, in Christ, shows us how we ought to live. Jesus behaves very differently by speaking the truth, humbly caring for others and confirming his words with a life well lived. We should follow him.
And here is a short talk based on the same passage: He Changed The World (Episode 26)