What is Repentance?

What is repentance? 

The term shubh, is most generally employed to express the Scriptural idea of genuine repentance. It is used extensively by the prophets, and makes prominent the idea of a radical change in one's attitude toward sin and God. It implies a conscious, moral separation, and a personal decision to forsake sin and to enter into fellowship with God. It is employed extensively with reference to man's turning away from sin to righteousness.
http://biblehub.com/topical/r/repentance.htm

"In those days John the Baptist came preaching in the wilderness of Judea, "Repent, for the kingdom of heaven is at hand." Matthew 3:1,2

Now after John was arrested, Jesus came into Galilee, proclaiming the gospel of God, and saying, “The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.” Mark 1:5,6

"So the disciples went out, telling everyone they met to repent of their sins and turn to God." mark 6:12

As these verses show, repentance was the theme of John, Jesus and his disciples.

Jesus also said, "I have not come to call the righteous but sinners to repentance." Luke 5:32
He didn't come to call those who thought they were good and doing alright. These people don't think they need to repent so how could they answer the call?  

"Or do you suppose that those eighteen on whom the tower in Siloam fell and killed them were worse culprits than all the men who live in Jerusalem? "I tell you, no, but unless you repent, you will all likewise perish." Luke 13:5

If we never repent of our sins - we will not be saved. We will perish, Jesus says. Not that he wants us to, but we will not be safe to take to heaven for we will not be one with God and we will bring a love of sin to heaven with us.

"Put all your rebellion behind you, and find yourselves a new heart and a new spirit. For why should you die, O people of Israel? For I have no pleasure in the death of anyone, declares the Lord GOD; so turn, and live.”Ezekiel 18:32