What is repentance? The literal Greek word, metanoia, has to do with changing your mind. But authentic repentance is much more than merely changing your opinion, your thought process, or your mood. It’s a complete spiritual about-face. And if it’s genuine, it will always result in a change of behavior, too.

And while true repentance is the flash point for saving faith, and a source of powerful, lasting assurance of that faith, it’s a widely misunderstood doctrine. Many believers only have a vague notion of what it means to repent, and they’re unfamiliar with what it looks like in the pages of Scripture.

Jesus’ parable in Matthew 21:28-30 is a classic illustration. “A certain man had two sons; and he came to the first, and said, Son, go work to day in my vineyard. He an­swered and said, I will not: but afterward he repented, and went. And he came to the second, and said likewise. And he answered and said, I go, sir: and went not” (KJV).

The response of the first son explains the meaning of repentance. He said, “I will not,” but he did. That’s repenting. He said one thing but changed his whole attitude and purpose and went the opposite way. Repentance is a complete change of heart and direction, not merely a new idea about something.

Peter preached repentance to the Israelites who gathered after he and the apostle John healed a lame man at the Temple gate in Jerusalem. Peter indicted the Israelites for ignoring the prophecies about Jesus, for labeling Him a blasphemer, and crucifying the very One who was sent to rescue them from their sins. But then Peter offered a solution: “Therefore repent and return, so that your sins may be wiped away” (Acts 3:19).

The nation of Israel had decided that God’s will for them was a self-generated righteousness. The Pharisees manipulated a system of legalism or works for righteous­ness. They made sure it maintained its hold over the people. If a Jew kept the 365 negative commands and the 248 positive commands of the law of Moses, he was safe and righteous. They thought that was what God wanted, and they rejected Jesus because of it.

Peter essentially said to them: You blew it on every count. Jesus is the very opposite of what you concluded Him to be. Therefore, reverse your decision and change course—turn all the way around. Whatever you think you’re doing to please God, if it isn’t based only on faith in Jesus Christ, stop doing it and turn around.

That’s repentance. It’s a total transformation from sin to salvation, from flesh to spirit. It’s a radical reversal of the orientation of your heart, and a new direction for your life.

But where does it come from? How does the Lord bring about this transformation, and how do we draw assurance from repentance? What does the act of repentance have to do with our confidence in an eternity with Christ?

Over the next several days, we’re going to answer those questions as we look further at the nature of genuine repentance.