Produce fruit in keeping with repentance [Matthew 3:8]
Jesus had some words of wisdom on this:
for a tree is recognised by its fruit."
There is wonderful exchange in the film ‘The Kingdom of Heaven’ when the knight-hero, Balian, is left to defend Jerusalem with untrained common people. The renegade bishop sneers that not being part of the noble elite, such people could not measure up; to which Balian responds by calling on all the men to kneel to be knighted.
‘Do you really think that calling someone a knight, will make him a better warrior?’ jeers the Bishop. ‘Yes!’ is Balian’s joyful response.
Jesus came to change our identity, to 'make the tree good'. The issue is what we choose to believe: our experience and history, or what God says:
For if, by the trespass of the one man, death reigned through that one man,
how much more will those who receive God's abundant provision of grace
and of the gift of righteousness reign in life through the one man, Jesus Christ!
You have been set free from sin and have become slaves to righteousness.
God made him who had no sin to be sin for us,
so that in him we might become the righteousness of God.
...put on the new self, created to be like God in true righteousness and holiness.
It will take time to change the habits of a lifetime, and when we fall, we know we can receive forgiveness [1 John 1:9]. But the foundation for change is a new identity - and that has been already been purchased for us on the Cross.