John the Baptizer's preaching of repentance is a watershed text on the definition of what repentance really is because it was a fulfillment of a prophecy recorded in Isaiah 40. (105) This is critically important because Jesus said we couldn't enter heaven without repenting, but people tell us all kinds of things about what their brand of repentance is.
John's message of repentance is easy to understand because he likens it to building a level highway in a mountainous land. The requirements of such a task involve cutting down the mountains and filling in the valleys. In analogical language, mountains refer to human pride, and valleys refer to human despair. God rejects both the proud and the despairing.
Because the proud believe, and act like, they do not need God and that their lives are their own to live as they please, in the pursuit of their own agenda. And the despairing believe, and act like, God is unwilling to be a Helper to them in the pursuit of His agenda. Both of these attitudes contradict, in fundamental ways, the clear declaration of the Word of God.
There is only one legitimate agenda for any human being to be involved in pursuing: God's, as it is revealed in the Bible. All other pursuits of all other agendas only generate chaos and death. God despises the agendas of death and He gives only opposition to those who are committed to them. Without repentance, those who pursue them will be met at the final gate by a God of wrath and anger. But the proud resist His agenda and seek to achieve their own goals in this life.
The despairing are no better. They may see that their agenda is of no real value, and they may see that God's is of supreme value. But they have tried to be good and failed, and have come to the belief that God is uninterested in helping them--and in some ways they are correct.
God isn't interested in helping us do His will if we, afterwards, believe that we had the ability to do this, and take the credit for it. God knows we are helpless in the face of the demands of holiness. But we don't know it. We think we are capable people. Yet, when we fail (as we often do), we think that God is at fault in our failure and we despair of His help. So, God refuses to respond to the despairing unless, and until, they reject their despair and believe in His promises.
Thus, repentance is fundamentally a faith issue: it approaches the issue of our life-agenda with three options before it. We can go our own way in our own strength; we can try to go His way in our own strength; or we can go His way in His strength. Repentance rejects both our way and our strength. Repentance embraces His agenda in the face of our weakness and His strength.
Thus, when John called for repentance, he was calling for a new way of looking at life. He was calling for a decision to humble ourselves before God and trust in His promises, His present willingness to help, and the wisdom of pursuing His agenda over our own. Without this, heaven will not be ours.