Jesus proclaimed a direct command and challenge to everyone He saw with this very command. He proclaimed the need to repent and reform. This was more than just changing your opinion or a particular belief. It is a change of heart, mind, and life.
The word for “repent” in this Gospel passage that Mark uses is the Greek word “metanoia.” This word does not simply mean to be sorry for our sins, as appropriate as this is. The word means literally to turn around and go in the opposite direction. It means “to amend with abhorrence of one's past sins.”
This repentance means to make a 180-degree turn in our lives when the direction we are going is leading us away from God. We must turn our backs on evil and sin. We should never give evil and sin a second-look. Just looking back at our lives before we encountered Jesus should be abhorrent enough to “not” want to go back.
The intention of this “180-degree turn” is to “stay turned” towards God and to never forsake God by returning or going back to our old sinful lifestyle and behaviors. Isaiah 55:6, "Seek the Lord while you can find him. Call on him now while he is near.”
The second thing Jesus commands besides repenting is to believe in the gospel. It is possible to change our direction, but not continue walking along the way of the Lord. If so, we are like the man who swept the trash out of his life, but never let himself be filled with God's Holy Spirit.
We must be careful not to become lazy in our faith and just start “dabbling” and messing around with our beliefs, Scripture or the things of God. This is “head knowledge without heart knowledge.” Luke 11:24-26, “When an evil spirit leaves a person, it goes into the desert, searching for rest. But when it finds none, it says, ‘I will return to the person I came from.’ So it returns and finds that its former home is all swept and in order. Then the spirit finds seven other spirits more evil than itself, and they all enter the person and live there. And so that person is worse off than before.”
Since he didn't fill his heart with the Holy Spirit, the things of the world, the flesh, and the devil filled the void in his life, and the final state of the man was worse than the first. 2 Peter 2:20-21, “Of course, you get no credit for being patient if you are beaten for doing wrong. But if you suffer for doing good and endure it patiently, God is pleased with you. For God called you to do good, even if it means suffering, just as Christ suffered for you. He is your example, and you must follow in his steps.”
We must both repent and believe. We must turn around, walk in the path of righteousness, keep walking, and fill our minds and hearts with Scripture and the things of God. Psalm 25:4-5, 8-9, “Show me the right path, O Lord; point out the road for me to follow. Lead me by your truth and teach me, for you are the God who saves me. All day long I put my hope in you… The Lord is good and does what is right; he shows the proper path to those who go astray. He leads the humble in doing right, teaching them his way.”
Metanoia! Let us all strive to turn our backs on sin and evil. Metanoia! Let us vow to never return to our old self and old ways of sinfulness no matter how familiar and comfortable those ways may have been. Let your "head knowledge" become "heart knowledge." Seek after God and never go back.