To repent is not to take on afflictive penances like fasting, vigils, flagellation, or whatever else appeals to our generosity. It means to change the direction in which you are looking for happiness.Thomas Keating
John's call for them to repent was an encouragement to give up on their dependence to the flesh: empire, their righteousness, and systems of reward and punishment. He wanted them, instead, to turn to God for their forgiveness.
John's ministry in the wilderness teaches that forgiveness isn't found in the temple with its divisions, walls, and exclusive access. It is found in the wilderness, in a trip across the Jordan, in which they relinquished everything to God and received forgiveness at no cost of their own.
It was a return back to the first days of Israel; a sort of reset at the Jordan. As they had passed through those waters many years before, John was calling them to embark on an Exodus from false-righteousness and the flesh.
May we too give up on trusting in our abilities and so-called religion and put our full trust in God. Go down to the Jordan and find true happiness and peace in God!