What is Repentance and why does it matter?

Repentance is a major theme in the Bible and often, if you know
the word, it can have negative connotations if you've been burned
by church or it brings to mind the guys on the street with the
loud speaker shouting at you as you pass. So how should we really
think about Repentance? What does Jesus have to say about it?
Let's explore it together!