If we asked a child 'what does it mean to repent?' chances are the response would be 'saying sorry'; chances are that we would get a similar response from many adults. At best the answer would add something like 'and promising (or trying) not to do it again', or 'turning over a new leaf'. Although such actions are commendable they fall far short of the Biblical concept of repentance.
The Old Testament concept of repentance is powerful and enlightening:
[1] God is said to repent (Genesis 6:6; Exodus 32:14; Jeremiah 18:8,10; Joel 2:13). This repentance or change of mind on God's part is (with the exception of Genesis 6:6) in relation to judgement, and conditional on a prior repentance or change of mind on the part of his people (Exodus 32:12; Jonah 3:10; Jeremiah 15:6; Joel 2:12,13). [Note: read all the above references in KJV if possible.]
[2] People are called to repent (Jeremiah 8:6; Ezekiel 14:6; 18:30), and commanded to turn (or return) to the Lord (Deuteronomy 30:2; Isaiah 31:6; 45:22; 55:6,7; Jeremiah 3:12ff; 3:22-4:1; 15:7; Hosea 6:1-3; 7:10,16). If we study the wider context in of these references we discover that the people had substituted idols for God. The call to repent or turn to the Lord was not made into a vacuum, nor was it made to a people who simply needed to clean up their act a bit. It was made to those who refused to acknowledge God as God. There was in some cases a superficial, physically visible acknowledgement of God, but God knew that this was fake. Neither heart nor mind nor will was in it. Heart, mind and will were, rather, totally rebellious against God.
Jeremiah describes this idolatrous rebellion against God with powerful images:
'Each pursues his own course like a horse charging into battle' (Jeremiah 8:6)
'They have forsaken me, the spring of living water,
and have dug their own cisterns,
broken cisterns that cannot hold water.' (Jeremiah 2:13b)
'Long ago you broke off your yoke
and tore off your bonds;
you said, 'I will not serve you!'
Indeed, on every high hill
and under every spreading tree
you lay down as a prostitute.' (Jeremiah 2:20)
The rebellion against God and his authority which characterised the first sin (Genesis 3) continues to characterise the human race. The call to repent is a call, a command, to personally reverse that original rebellion. The call to repent is a call to return to God, to come back under his authority, to acknowledge that he alone, not the idols, not myself, has sole right to be Lord of my life. It is only when this total about-turn repentance has taken place that the promise of forgiveness and acceptance is given:
'Seek the Lord while he may be found;
call upon him while he is near.
Let the wicked forsake his way
and the evil man his thoughts.
Let him turn to the Lord,
and he will have mercy on him,
and to our God, for he will freely pardon.' (Isaiah 55:6,7)
This is not some airy-fairy, abstract 'seeking' and 'turning to' the Lord, but practical, down to earth, grass roots seeking of the Lord , and turning to the Lord , instead of whatever has usurped his place. In this command to repent I am commanded to stop turning my back on God. When I thus repent, I am promised his mercy and pardon. The blessing of salvation is granted only to those who repent (Hosea 14).
In the New Testament the idea of change is inextricably involved in repentance. The Greek word is metanoeo. The prefix, meta, indicates change. Noeo means I think or perceive, and has the same root as nous meaning mind. Repentance, then, is an act in which I change my mind, in which I under-go a complete turn-around in the way I think about and perceive reality, particularly in the way in which I perceive and think about God, myself, and my sin. As in the Old Testament, repentance is the reversal of the Genesis 3 rebellion against God and God's authority.
In the New Testament:
Both John the Baptist and Jesus said: 'Repent, for the kingdom of heaven is near.' (Matthew 3:2; 4:17). How has the kingdom of heaven drawn near? It has drawn near because Jesus Christ, the eternal King, has come to us. When we stand confronted by Jesus Christ we stand in the presence of the King, to whom all authority has been given, (Matthew 28:18) and before whom every knee must bow (Philippians 2:9-11). The one appropriate response in the presence of the King is submission. The only alternative is continuing rebellion against his authority. Either I change my mind about him and submit to his Lordship, or I continue in my stubborn-minded rejection of his right to rule me. There is no middle ground.
This greatness of Jesus Christ is highlighted in Matthew 11:20-24, 12:39-42 and Luke 10:8-15. Here Jesus points out the terrible fate of those who have refused to repent on hearing his teaching. So great is he, so significant, that there can be no forgiveness of sin for those who refuse to respond either to his word, or to the truth spoken about him. Such refusal is actually rejection of God the Father (Luke 10:16).
In Acts 2:22-38 the focus of Peter's message is the true identity of Jesus Christ. Confronted by the fact that the man they crucified is indeed the Lord, with the right to make all the claims for which they had crucified him, the Jews cry out 'Brothers, what shall we do?' Peter replied: 'Repent ... '. Change your mind. Admit that he is the one he claimed to be. Throw out your own perceptions of what God is, of who God is, and acknowledge that here, in this man, Jesus of Nazareth, is your God (Isaiah 40:9). That is what Thomas did (John 20:28). That is what Saul did (Acts 9:1-31). Saul's conversion is a clear example of the New Testament concept of repentance. Here we see a man do a complete about-face. Here we see a man, confronted by the Lord Jesus Christ, undergo a complete change of mind about who Jesus is, and a subsequent complete reorientation of his whole life on the basis of this changed understanding of God.
There is no back door into the kingdom of heaven. Because Jesus Christ is the only way (John 14:6), and the only way in (John 10:7), we cannot side step this act of repentance. We can only gain salvation by acknowledging him as our God. We cannot sneak into heaven behind his back. We can only gain salvation by admitting that all of our own god-concepts are wrong; that we are wrong when we think that we can be boss of our own lives; that we are wrong when we think it's okay to live how we please. Forgiveness of sin is only promised to those who thus repent (Luke 13:3; Acts 3:19; 2 Peter 3:9). [This will be pursued further in the study on 'Faith'.]
John the Baptist made this clear (Matthew 3:7-10, Luke 3:7-14). Jesus repeatedly stressed its importance. He gave no credibility to a profession of faith which did not produce a changed life (Matthew 7:15-23, 24-27). He disowns 'sheep' who do not listen to his voice and follow him (John 10:3,4,16,27). He identifies as genuine only that love for him which also obeys his commands (John 14:15,21,23; 15:14). He never sees submission to his authority as optional, but as an essential expression of genuine repentance and faith.
Although it is obvious that repentance is the necessary human response to the Gospel of Jesus Christ, we must not assume that it is within the ability of our own hearts, minds and wills to do it. The Bible teaches that our hearts are deceitful and beyond cure (Jeremiah 17:9), that our minds are blinded (2 Corinthians 4:4), and that our wills are powerless (John 6:44; 15:5; Romans 5:6). For this reason the New Testament teaches that repentance, like every other aspect of salvation, is a gift of God (Acts 5:31; 11:38; Romans 2:4; 2 Timothy 2:25).