In Mission in Christ's Way Lesslie Newbigin (d. 1996), long-time missionary to India, writes about the true meaning of repentance:

I remember once visiting a village in the Madras diocese. There was no road into the village; you reached it by crossing a river, and you could do this either on the south side of the village or on the north. The congregation had decided that I would come by the southern route, and they had prepared a welcome such as only an Indian village can prepare. There was music and fireworks and garlands and fruit and silumbum (the performance of a South Indian martial art done on ceremonial occasions) —everything you can imagine. Unfortunately I entered the village at the north end and found only a few goats and chickens. Crisis! I had to disappear while word was sent to the assembled congregation, and the entire village did a sort of U-turn so as to face the other way. Then I duly reappeared.

This is what metanoia means. The TEV translation gives a misleading impression by translating it: "Turn away from your sins." That might make it look like a traditional call for moral reformation. That is not the point. There is nothing about sins in the text (Mark 1:14-18). The point is: "The reign of God has drawn near, but you can't see it because you are looking the wrong way. You are expecting the wrong thing. What you think is 'God' isn't God at all. You have to be, as Paul says, transformed by the renewing of your mind. You have to go through a mental revolution; otherwise the reign of God will be totally hidden from you."